A method of constructing a steel trestle

Abstract

A kind of construction method of steel trestle, the construction method of the temporary bridge construction technical field, construction method includes abutment foundation construction, abutment body construction, abutment coping construction, backfill, bailey beam installation, bridge deck installation and guardrail installation etc.The unique process parameters of each stage construction design of the present application ensure the construction quality of each stage, especially the stability of concrete beam design can be well guaranteed to expand base and subsequent pouring abutment body, after construction and subsequent traffic use, displacement, deflection will not occur under the impact of larger external force, can greatly improve the service life, and improve bearing capacity;Design embedded part is "Guan" type, can well guarantee the connection stability of abutment body and abutment coping;Design bailey beam additional longitudinal i-beam can effectively increase the overall stability and safety of trestle;Design bridge lane both sides welded double i-beam, can effectively prevent wheel from sliding off bridge deck, also will further assist to improve the deformation resistance of bridge deck.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of temporary bridge construction, and particularly relates to a construction method of a steel trestle bridge. BACKGROUND

[0002] A trestle bridge is a temporary bridge structure, and is divided into a wood trestle bridge and a steel trestle bridge according to the materials used. The steel trestle bridge refers to a bridge erected by steel, has the characteristics of simple structure, convenient transportation, quick erection, large load capacity, good interchangeability and strong adaptability, and is the most widely used assembled load-bearing component in China. According to the structural characteristics of the steel trestle bridge, the steel trestle bridge structure can be conveniently adjusted to meet the different local bearing capacity requirements.

[0003] In the construction process of a river-crossing bridge, a steel trestle bridge is usually constructed in parallel with the main bridge to transport various construction materials and mechanical equipment.

[0004] In order to ensure the overall stability of the steel trestle bridge, meet the bearing capacity, and resist the impact of floods, different forms of steel trestle bridges need to be constructed, and therefore the construction methods are different, which are specifically manifested in the construction of abutment foundations, abutments, bailey beams, bridge decks and guardrails. Each step of construction plays an important role in the final performance and service life of the bridge.

[0005] At present, most of the steel trestle bridges are greatly affected by seasonal changes, day and night temperature differences, ice and snow melt water, rainfall, underground water and the like after construction, so that the steel trestle bridges are corroded and deformed, the load-bearing performance is reduced, and even the foundations, abutments or bridge decks are collapsed, cracked or broken, which greatly reduces the service life. Especially for the environment with short spring and autumn seasons, long winter and summer seasons, large changes in temperature, large day and night temperature differences, long sunshine hours and large extreme temperature changes, the service performance of the steel trestle bridge needs to be improved, and the construction method needs to be improved to meet the service performance and life of the steel trestle bridge in the harsh environment. SUMMARY

[0006] The existing steel trestle is susceptible to environmental influence, shortens service life, and is not suitable for long-term use in harsh environment. The present application provides a construction method of steel trestle, unique process parameters in each stage of construction design ensure the construction quality of each stage, especially the concrete beam design can well ensure the stability of the expanded foundation and the subsequent pouring of the pier body, after construction and subsequent use, large external force side impact will not cause displacement and deflection, which can greatly improve the service life and bearing capacity; the design of the embedded part is a "bird" type embedded part, which can well ensure the connection stability of the pier body and the pier cap, thereby improving the bridge bearing capacity, reducing deformation and fracture during use, and prolonging the service life; the design uses the horse bolt to lock the bailey beam and the two side longitudinal I-beams, and the additional longitudinal I-beam can effectively increase the overall stability and safety of the trestle; the design welds double I16 steel on both sides of the bridge deck, which can effectively prevent the wheels from sliding off the bridge deck, has higher safety, and can further assist in improving the anti-deformation capacity of the bridge deck. The steel trestle construction method can prepare a trestle with high bearing capacity and long service life, especially for the use performance in harsh environment, which is not susceptible to the influence of factors such as seasonal change, long winter and summer seasons, large diurnal temperature difference, long sunshine duration, large extreme temperature change, ice and snow melt water, rainfall, underground water, etc. The specific technical scheme is as follows:

[0007] A construction method of steel trestle, comprising the following steps:

[0008] S1, abutment foundation construction:

[0009] S1.1, foundation pit excavation: excavate the foundation pit by excavator, when the foundation pit is excavated to 20cm above the base elevation, excavate by hand, and over-excavation is strictly prohibited; drainage ditches and water collection wells are arranged around the foundation pit to timely pump out the water in the foundation pit to prevent the foundation pit and base from being soaked; for the foundation pit submerged by ground water, build cofferdams, change rivers, change ditches, and build dams, and then excavate after the ground water is discharged; the foundation pit excavation cannot be interrupted, and after the design elevation is reached and passes the inspection, the foundation is immediately poured.

[0010] When the abutment is arranged on the water surface, and the water depth is more than 1.5m, the flow rate is within 0.5m / s, the river bed soil has small water permeability and meets the flood discharge requirement, the soil cofferdam is built; before building the soil cofferdam, the tree roots, stones and other sundries at the river bed of the dam bottom are removed clean, the cofferdam material adopts cohesive soil or sand mixed with clay, and the cofferdam is built from the upstream to the downstream closure, and is tamped after exceeding the water surface; when the outer slope of the cofferdam is in danger of being scoured by water, the anti-scouring material is used for protection.

[0011] When the water-free soil foundation pit bottom surface, the design plane size of the foundation is widened by not less than 50cm on each side, the vertical excavation is performed without setting formwork.

[0012] When there is a water and soil foundation pit bottom, set up drainage ditch and catchment well, according to the basis design plane size each side is widened not less than 80 cm; the basement avoids over-excavation, the loose part is removed; when using mechanical excavation, the structure of the basement soil should not be damaged, a certain protective layer is reserved above the design elevation 20 cm, and then excavated by manual.

[0013] After the foundation is excavated, the bearing capacity test of the foundation is carried out, when the bearing capacity of the foundation is less than the design requirement, the foundation is treated by replacement, the replacement depth is not less than 50 cm, the treatment range is 50 cm wider than the bottom of the foundation, after the replacement is completed and compacted, the next process construction is carried out after the inspection is qualified.

[0014] S1.2, cushion pouring: after the foundation pit is inspected and qualified, a 10-12 cm thick C20 concrete cushion is poured on the basement, which is used to protect the basement and make the basement surface flat, easy to bind reinforcement and install formwork.

[0015] S1.3, formwork installation: the formwork adopts customized steel formwork, fastener type steel pipe scaffold, and crane lifting; the surface of the formwork is smooth and not easy to deform, the joint between the formworks is tight and does not leak mortar, and there is no step, in order to ensure that the joint does not leak mortar during construction, 2-3 mm rubber or sponge is added to the joint of the formwork to effectively prevent mortar leakage, and ensure that the concrete surface is beautiful and the lines are smooth; before assembling the formwork, the surface of the formwork is polished flat with a sander, cleaned and coated with long-acting release agent; before pouring the concrete, the planar position, top elevation, node connection and longitudinal and transverse stability of the formwork are checked, and the pouring of the concrete can be carried out after confirmation.

[0016] S1.4, expanded foundation concrete pouring: the pouring of the concrete adopts "chute method" or "pumping method" construction, in the process of pouring the concrete, the slump of the concrete is fully considered, and the free falling height of the concrete is controlled to be not more than 2 m, and when it is higher than 2 m, chute is matched for pouring, so as to avoid segregation.

[0017] The concrete is continuously poured, before pouring each section of concrete, a prefabricated concrete beam with a cross section of an equilateral triangle is placed at the edge of the expanded foundation, the distance between the concrete beam and the edge of the expanded foundation is 5-10 cm; the height of the concrete beam is 3-6 cm, and the length of the concrete beam is equal to the width of the pouring surface; after the pouring of each section of concrete is completed, the concrete is poured horizontally in layers within the full cross section, the thickness of the pouring layer is controlled to be within 30 cm, and the longest interval is not more than the initial setting time of the concrete; the concrete is vibrated by inserting type vibrator, the moving interval of the vibrator is not more than 1.5 times of the action radius of the vibrator, and the vibrator is inserted into the lower layer by 5-10 cm; the vibration is uniform, and the steel bars and formwork should not be touched; the sign of vibration compaction is that the concrete stops sinking, no more bubbles come out, the surface is flat and smooth, and the vibration duration is 10-20 s.

[0018] After the concrete is poured, the concrete surface shall be promptly trimmed, the slurry shall be collected and leveled, and after the slurry is set and the concrete has hardness, the second surface finishing shall be carried out; the joint of the abutment shall be roughened to expose the large granular stones in the concrete to ensure good connection between the abutment and the enlarged foundation concrete.

[0019] S1.5, Foundation maintenance: Remove the formwork when the concrete strength reaches 2.5 Mpa. After the concrete begins to set, cover it with geotextile and sprinkle water for maintenance to ensure that the concrete surface is fully moist; when the ambient temperature is lower than 5°C, insulate the concrete surface and prohibit direct sprinkling of water on the concrete for maintenance. The maintenance time shall not be less than 7 days.

[0020] S2, Abutment body construction:

[0021] S2.1, Construction survey: Release each control point of the abutment on the top surface of the foundation concrete, and use ink lines to pop out the plane position of the abutment. The ink lines shall exceed the formwork lines so as to correct the formwork, erect the scaffolding, install the protective railing and safety net, and erect the operation platform when installing the formwork.

[0022] S2.2, Formwork installation: Install the formwork at the plane position of the abutment popped out by the ink lines on the top surface of the foundation concrete, adjust the top surface of the formwork to be horizontal, and fill the gap between the formwork and the foundation concrete with M10 mortar to prevent slurry leakage during the pouring of the abutment body concrete.

[0023] S2.3, Abutment body concrete pouring: The abutment body is constructed in layers, with each layer height being 2 m; the concrete is C30 concrete. When pouring the concrete, the concrete is poured in horizontal layers, and the layer thickness shall not be greater than 30 cm; the concrete is vibrated with an inserted vibrator, and the vibration duration of each vibration point is 20 - 30 s until the concrete stops sinking, no bubbles appear, and floating slurry appears on the surface of the bubbles; after the concrete is poured, the concrete surface shall be promptly trimmed, the slurry shall be collected and leveled, and after the concrete sets and hardens, the second surface finishing shall be carried out; pour in layers until the position 60 cm away from the top of the abutment body, and embed the embedded parts into the concrete to facilitate the subsequent connection between the embedded parts and the reinforced concrete part of the abutment cap.

[0024] The embedded part is a "π" - shaped embedded part.

[0025] S3, Abutment cap construction:

[0026] At the connection between the abutment cap and the abutment body, the formwork shall fit tightly with the abutment body without slurry leakage; the steel bars of the abutment cap are welded to the embedded parts. When welding the steel bars of the abutment cap, avoid bending at the joints of the steel bars. Pour the abutment cap concrete in the order of pouring the mid - span first and then the cantilever, gradually approaching the fulcrum; carry out two surface finishes on the concrete surface before the concrete begins to set and sprinkle water for maintenance.

[0027] S4, Abutment backfill:

[0028] When the concrete strength of the abutment reaches 75% or more, backfill material is carried out to ensure the stability of the wall. The backfill soil is gravelly soil. The backfill layer thickness and compaction are strictly controlled. The maximum loose thickness of each layer of fill material is no more than 20cm. During compaction, the wall should not be affected by impact. Within 1.0 meter of the back of the wall, small compaction equipment such as frog rammer, internal combustion rammer or hand-held vibratory roller is used for compaction. The compaction degree of the backfill soil is not less than 96%.

[0029] S5, Bailey beam installation:

[0030] The Bailey bridge is pre-assembled on land according to the design. Considering that the deflection of the Bailey bridge mainly comes from the tension and compression of the gap between the pin holes, the Bailey pins are manually hammered with a large iron hammer during installation to ensure that the Bailey pins are tightly inserted into the pin holes, and safety pins are inserted to avoid leaving gaps. After the Bailey bridge is assembled, it is directly lifted into place by a crane, and the upper and lower reinforcing chords of the Bailey truss are installed. The Bailey bridge and the longitudinal I-beams on both sides are locked with U-bolts to increase the overall stability and safety of the temporary bridge. After the Bailey bridge is installed, the transverse distribution beams of the I-beams are installed with a spacing of 30±5cm, and the transverse I-beams are locked to the Bailey bridge with U-bolts.

[0031] The Bailey truss has supporting flower racks installed within the truss segments.

[0032] S6, bridge deck mounting:

[0033] The bridge deck is supported on reinforced Bailey beams and securely connected to the Bailey panels with U-bolts.

[0034] The steel trestle bridge has a clear width of 4 to 6 meters. The bridge deck uses standard steel bridge deck and is fixed to Bailey beams with U-bolts. Drainage holes are set on the bridge deck to ensure that water does not accumulate. Water is diverted into the river from both sides of the abutment to avoid water accumulation on the bridge.

[0035] S7, Guardrail Installation:

[0036] After the bridge deck is installed, double I16 I-beams are welded on both sides of the lane to prevent the wheels from slipping off the bridge deck; the guardrails are made of 30*3mm square tubes, with a height of 1.3 to 1.5m, a vertical pole spacing of 0.8 to 1m, and a horizontal pole spacing of 0.4 to 0.5m.

[0037] The construction method for a steel trestle bridge of the present invention has the following advantages compared with the prior art:

[0038] I. The construction method for the steel trestle bridge of this invention involves initial mechanical excavation of the foundation pit, followed by manual excavation when the pit reaches 20cm above the base elevation. This method effectively prevents over-excavation, which necessitates backfilling. Backfilling loosens the soil, compromising foundation stability and consequently affecting the bridge's overall stability. Furthermore, the foundation pit excavation must be continuous, with concrete poured promptly upon reaching the required elevation. To maximize construction quality and minimize backflow from the surrounding water collection wells, the method ensures the bridge's overall quality.

[0039] II. The steel trestle bridge construction method of this invention designs drainage ditches and collection wells around the foundation pit. When the foundation pit is flooded by surface water, a cofferdam is built, the river or ditch is changed, or a dam is built to drain the surface water before excavation, so as to prevent the foundation pit and the base from being soaked by water and affecting the stability of the foundation.

[0040] 3. When the bridge abutment is located on the water surface, and the water depth exceeds 1.5m, the flow velocity is less than 0.5m / s, and the riverbed soil has low permeability and meets the flood discharge requirements, an earthen cofferdam should be constructed. The cofferdam material should be cohesive soil or sand-clay mixture, starting from the upstream and ending at the downstream closure point, and compacted after exceeding the water surface. This invention uses cohesive soil or sand-clay mixture, and compacts it after exceeding the water surface, which can effectively ensure the water resistance and collapse resistance of the earthen cofferdam, ensuring that the bridge construction can proceed safely and smoothly within the construction period.

[0041] Fourth, when the bottom of the foundation pit is in a dry soil condition, the foundation design plane dimensions are widened by no less than 50cm on each side, and vertical excavation is carried out without the use of formwork. The design of this invention without the use of formwork can reduce the construction period, improve work efficiency, shorten the foundation excavation cycle, and ensure rapid and continuous construction to the greatest extent possible.

[0042] 5. When the foundation bearing capacity is less than the design requirements, the foundation shall be replaced. The replacement depth of this invention shall not be less than 50cm, and the treatment range shall extend more than 50cm beyond the bottom of the foundation, so as to ensure the quality of replacement and ensure that the foundation bearing capacity meets the construction requirements.

[0043] VI. The steel trestle bridge construction method of the present invention is designed to pour a C20 concrete cushion layer with a thickness of 10-12cm on the base to protect the base and make the base surface flat, and to facilitate the binding of steel bars and the installation of formwork.

[0044] 7. During formwork installation, in order to ensure that the joints do not leak grout during construction, the present invention adds 2-3mm of rubber or sponge to the formwork joints; this ensures the tightness of the formwork installation, prevents the inner and outer sides of the formwork from penetrating each other, and thus ensures the quality of concrete pouring.

[0045] 8. During concrete pouring, the slump of the concrete should be fully considered, and the free fall height of the concrete should be controlled. The construction method of this invention is designed to control the fall height to no more than 2m. If the fall height exceeds 2m, a chute should be used in conjunction with the pouring to prevent segregation. The design of this invention involves roughening the concrete at the abutment joint to expose large aggregate particles in the concrete, which can effectively ensure a good connection between the abutment and the spread foundation concrete and improve the quality of the connection.

[0046] 9. In the construction method of this invention, when pouring the concrete for the enlarged foundation, before pouring each section of concrete, a precast concrete rib with an equilateral triangular cross-section is placed at the edge of the enlarged foundation ring, 5-10cm away from the edge of the enlarged foundation; the height of the concrete rib is 3-6cm, and the length of the concrete rib is equal to the width of the pouring surface; this concrete rib design can effectively ensure the stability of the enlarged foundation and the subsequently poured platform, and after construction and subsequent use, it will not displace or deviate when subjected to large external lateral impacts, which can greatly improve the service life and the load-bearing capacity.

[0047] 10. This invention designs continuous concrete pouring. After each section of foundation concrete is poured in one go, the concrete is poured horizontally in layers across the entire flat cross-section, with each layer thickness controlled within 30cm and the longest interval not exceeding the initial setting time of the concrete. Concrete vibration is achieved using an immersion vibrator, with the vibrator's movement distance not exceeding 1.5 times its effective radius, and the vibrator inserted 5-10cm into the lower layer. Vibration must be uniform, ensuring no missed areas and avoiding contact with reinforcing bars and formwork. The sign of complete compaction is that the concrete stops settling, no more air bubbles emerge, and the surface becomes flat and smooth with a layer of cement paste. The vibration time is 10-20 seconds. This parameter design ensures the quality of each layer of concrete, thereby guaranteeing the quality of each section of concrete.

[0048] XI. The construction method of this invention designs the bridge abutment body for layered construction, with each layer being 2m high; C30 concrete is used, and the concrete is poured in horizontal layers with a layer thickness not exceeding 30cm; the concrete is vibrated using an immersion vibrator, with each vibration point lasting 20-30 seconds, until the concrete stops settling, no air bubbles appear, and laitance appears on the surface of the air bubbles; after the concrete is poured, the concrete surface is promptly trimmed, smoothed, and leveled, and a second finishing is performed after the concrete has hardened; this pouring parameter design ensures the quality of the bridge abutment body concrete pouring.

[0049] 12. The construction method of this invention involves pouring the bridge abutment body in layers until 60cm remains from the top of the abutment body, then embedding the pre-embedded parts into the concrete to facilitate the subsequent connection between the pre-embedded parts and the reinforced concrete part of the abutment cap; the pre-embedded parts are designed as "U"-shaped pre-embedded parts, which can effectively ensure the connection stability between the abutment body and the abutment cap, thereby improving the load-bearing capacity of the bridge, making it less prone to deformation and breakage during use, and extending its service life.

[0050] Thirteen, the construction method of this invention is designed so that the formwork and the abutment body are tightly fitted at the connection between the abutment cap and the abutment body to prevent grout leakage. The steel bars of the abutment cap are welded to the embedded parts. When welding the steel bars of the abutment cap, bending at the joint of the steel bars is avoided. The concrete of the abutment cap is poured in the order of pouring the mid-span first and then the cantilever, gradually moving towards the support. This construction method design can further improve the quality of the bridge and make it less prone to cracking, deformation and breakage.

[0051] XIV. In the construction method of this invention, backfilling of the abutment is limited to when the concrete strength of the abutment body reaches 75% or more, ensuring the stability of the wall. The backfill soil is gravelly soil, and the layer thickness and compaction are strictly controlled. The maximum loose thickness of each layer is no more than 20cm. During compaction, the wall body should not be subjected to impact. Within 1.0 meter of the wall backfill, small compaction equipment such as frog-type rammers, internal combustion rammers, or hand-held vibratory rollers are used for compaction, and the compaction degree of the backfill soil is not less than 96%. This construction parameter design can effectively guarantee the quality of backfilling, thereby improving the service life of the steel trestle bridge abutment.

[0052] 15. During the installation of Bailey bridges, the design involves manual hammering with a large iron hammer to ensure that the Bailey pins are tightly inserted into the pin holes, and then inserting safety pins to avoid leaving gaps and ensure installation quality. In addition, the design uses U-bolts to lock the Bailey bridges and the longitudinal I-beams on both sides. The additional longitudinal I-beams can effectively increase the overall stability and safety of the temporary bridge.

[0053] Sixteen, the design incorporates double I16 I-beams welded to both sides of the bridge deck lanes, which effectively prevents wheels from slipping off the bridge deck, enhancing safety and further improving the bridge deck's resistance to deformation.

[0054] In summary, the steel trestle bridge construction method of this invention can produce temporary bridges with high load-bearing capacity and long service life, especially in harsh environments. It is less affected by seasonal changes, long winters and summers, drastic temperature variations, large diurnal temperature differences, long hours of sunshine, significant extreme temperature fluctuations, snowmelt, rainfall, and groundwater. In the mid-latitude continental arid climate, spring and autumn are short, while winters and summers are long. Temperature variations are drastic, with large diurnal temperature differences, long hours of sunshine, and abundant heat. The average temperature in the warmest months of July and August is 25.7℃, and the average temperature in the coldest month of January is -15.2℃. Extreme temperatures range from a maximum of 40℃ to a minimum of -40℃. There are localized sections within the pipeline where snow is blown in. The river generally runs north-south, with an average annual runoff of 244 million m³. The water volume is significantly affected by the season, primarily originating from snowmelt, rainfall, and groundwater. The flood season is from May to September each year. With an average annual precipitation of 194 mm, an average annual evaporation of 2616.9 mm, an average annual frost-free period of 179 days, and an average annual sunshine duration of 2813.5 hours, and given the geological conditions at the bridge site, which are mainly composed of breccia, pebble soil, strongly weathered tuff, and moderately weathered marl, the steel trestle bridge did not experience any displacement, collapse, cracking, or breakage after 12 months of use, demonstrating its excellent practicality. Attached Figure Description

[0055] Fig. 1 This is a top view of the embedded parts used in the construction method of a steel trestle bridge according to Embodiment 1 of the present invention;

[0056] Fig. 2 This is a side view of the embedded parts used in the construction method of a steel trestle bridge according to Embodiment 1 of the present invention. Detailed Implementation

[0057] The following are specific implementation cases and appendices. Figs. 1-2 The present invention will be further described, but the present invention is not limited to these embodiments.

[0058] A certain expressway has a length of approximately 30.885 km, including 27 bridges, 112 culverts, and a main roadbed length of 25.5 km. Bridges account for approximately 17.4% of the main road. The entire line includes 2 interchanges and 1 service area.

[0059] The project adopts an upper-bearing steel trestle bridge, which is arranged at mileage chainage K32+900 (Example 1), mileage chainage K33+200 (Example 2), mileage chainage K33+300 (Example 3), and mileage chainage K26+700 (Example 4) to serve as a temporary access road for the bridge construction across the river.

[0060] The construction section, from approximately K2+500 to K15+000, is characterized by a flat, open piedmont plain with an elevation of 1200-1400 meters. From K15+000 to K30+000, the area is hilly, with the route primarily following the mountainside. From K30+000 to the end of the project, the route enters a mountainous canyon landscape, with the elevation rising to approximately 1900 meters. The region has a typical mid-latitude continental arid climate, with short spring and autumn seasons and long winter and summer seasons. Temperatures fluctuate dramatically, with large diurnal temperature variations, long hours of sunshine, and abundant heat. The average temperature in the warmest months of July and August is 25.7℃, while the average temperature in the coldest month of January is -15.2℃. Extreme temperatures range from a high of 40℃ to a low of -40℃, with some sections experiencing blowing snow. The rivers generally run north-south, with an average annual runoff of 244 million cubic meters. 3 Water volume is greatly affected by the season, mainly from snowmelt, rainfall, and groundwater. The flood season is from May to September each year. The average annual precipitation is 194 mm, the average annual evaporation is 2616.9 mm, the average annual frost-free period is 179 days, and the average annual sunshine duration is 2813.5 hours. The geological lithology of the bridge site is mainly composed of breccia, pebble soil, strongly weathered tuff, and moderately weathered marl. The design load of the steel trestle bridge is: the total weight of a single vehicle shall not exceed 75t, the distance between vehicles shall not be less than 10m, and the speed limit is 20km / h.

[0061] Example 1

[0062] The steel trestle bridge is located at kilometer marker K32+900, with a length of 30 meters and a net width of 4.5 meters.

[0063] A construction method for a steel trestle bridge includes the following steps:

[0064] S1, Bridge abutment foundation construction:

[0065] S1.1, Excavation of the foundation pit: The foundation pit shall be excavated by excavator. When the foundation pit is excavated to 20cm above the base elevation, manual excavation shall be adopted. Over-excavation is strictly prohibited. Drainage ditches and sump pits shall be set up around the foundation pit to pump out the water in the foundation pit in time to prevent the foundation pit and base from being soaked. In the case of foundation pits that are flooded by surface water, cofferdams shall be built, rivers or ditches shall be diverted, or dams shall be built to drain the surface water before excavation. The excavation of the foundation pit shall not be interrupted. After the design elevation is reached and the inspection is qualified, the foundation shall be poured immediately.

[0066] When the bridge abutment is set on the water surface, and the water depth exceeds 1.5m, the flow velocity is less than 0.5m / s, and the riverbed soil has low permeability and meets the flood discharge requirements, an earthen cofferdam should be built. Before building the earthen cofferdam, tree roots, stones and other debris at the bottom of the riverbed should be removed. The cofferdam material should be cohesive soil or sand mixed with clay. The construction should start from the upstream and end at the downstream, and be compacted after it exceeds the water surface. If there is a risk of water erosion on the outer slope of the cofferdam, erosion-resistant materials should be used for protection.

[0067] When the bottom of the foundation pit is made of dry soil, the width on each side should be increased by no less than 50cm according to the foundation design plane dimensions, and vertical excavation should be carried out without erecting formwork.

[0068] When there is water in the foundation pit, drainage ditches and collection wells should be set up, and the width on each side should be not less than 80cm according to the foundation design plane dimensions; over-excavation of the foundation should be avoided, and loose parts should be removed; when using mechanical excavation, the structure of the foundation soil should not be damaged, and a certain protective layer should be retained 20cm above the design elevation, and then manual excavation should be carried out.

[0069] After the foundation is excavated, a bearing capacity test is conducted on the foundation. If the bearing capacity of the foundation is less than the design requirements, the foundation is replaced with filler. The replacement depth is not less than 50cm, and the treatment range extends 50cm beyond the bottom of the foundation. After the replacement is completed and compacted, the next construction procedure is carried out after the inspection is passed.

[0070] S1.2, Subbase pouring: After the foundation pit passes inspection, pour a 10cm thick C20 concrete subbase on the foundation, spread and level it to protect the foundation and make the foundation surface flat, making it easy to tie steel bars and install formwork.

[0071] S1.3, Formwork Installation: Custom-made steel formwork is used, along with coupler-type steel pipe scaffolding and truck crane hoisting. The formwork surface is flat, smooth, and not easily deformed. The joints between formwork panels are tight, leak-proof, and without steps. To ensure no grout leakage during construction, 2mm rubber or sponge pads are added to the formwork joints to effectively prevent leakage and ensure a beautiful concrete surface and smooth lines. Before assembling the formwork, the surface is first ground smooth with a grinder, cleaned, and coated with a long-lasting release agent. Before pouring concrete, the formwork's plane position, top elevation, joint connections, and longitudinal and transverse stability are checked and confirmed before concrete can be poured.

[0072] S1.4, Enlarged foundation concrete pouring: The concrete is poured using the "chute method" or "pumping method". During the concrete pouring process, the slump of the concrete is fully considered, and the free fall height of the concrete is controlled to be no more than 2m. If it is higher than 2m, a chute is used to assist in the pouring to avoid segregation.

[0073] For continuous concrete pouring, before each section of concrete is poured, a precast concrete rib with an equilateral triangular cross-section is placed at the edge of the enlarged base ring, 5cm away from the edge of the enlarged base. The height of the concrete rib is 3cm, and the length of the concrete rib is equal to the width of the pouring surface. After each section of foundation concrete is poured in one go, the concrete is poured horizontally in layers within the entire flat cross-section, with the thickness of each layer controlled within 30cm, and the longest interval not exceeding the initial setting time of the concrete. The concrete is vibrated using an immersion vibrator, with the vibrator moving at intervals not exceeding 1.5 times the vibrator's radius of action, and inserted 5-10cm into the lower layer. Vibration must be uniform, without any missed areas, and without touching the reinforcing bars or formwork. The sign of compacted concrete is that the concrete stops settling, no more air bubbles emerge, the surface is flat and glossy, and the vibration time is 10-20 seconds.

[0074] After the concrete is poured, the concrete surface should be repaired and smoothed in a timely manner. After the concrete has hardened, a second smoothing should be carried out. The joints of the bridge abutment should be roughened to expose the large stones in the concrete, so as to ensure a good connection between the bridge abutment and the spread foundation concrete.

[0075] S1.5, Basic curing: Remove the formwork after the concrete strength reaches 2.5 MPa. After the concrete has initially set, cover it with geotextile and sprinkle water for curing to ensure that the concrete surface is fully moist. When the ambient temperature is below 5℃, insulate the concrete surface and prohibit direct watering of the concrete for curing. The curing time shall not be less than 7 days.

[0076] S2, Bridge abutment construction:

[0077] S2.1, Construction Survey: Mark each control point of the bridge abutment on the top surface of the foundation concrete, and use an ink line to mark the plane position of the bridge abutment. The ink line should extend beyond the template line so that the template can be corrected, scaffolding can be erected, guardrails and safety nets can be installed, and a working platform can be set up during the installation of the template.

[0078] S2.2, Template Installation: Install the template at the position of the bridge abutment plane marked by the ink line on the top of the foundation concrete. Adjust the top surface of the template to be level. Fill the gap between the bottom of the template and the foundation concrete with M10 mortar to prevent grout leakage during the pouring of the abutment concrete.

[0079] S2.3, Casting of pier concrete: The pier is constructed in layers with each layer having a height of 2 m. C30 concrete is used. When casting the concrete, it is cast horizontally in layers with the layer thickness not exceeding 30 cm. The concrete is vibrated using an insertion vibrator. The vibration duration for each vibration point is 20 - 30 s until the concrete stops sinking, no bubbles appear, and a floating slurry appears on the surface of the bubbles. After the concrete is cast, the concrete surface is promptly trimmed, tamped, and leveled. After the concrete has set and hardened, it is tamped again. When casting in layers up to a position 60 cm remaining from the top of the pier, the embedded parts are embedded into the concrete to facilitate the subsequent connection between the embedded parts and the reinforced concrete part of the pier cap.

[0080] The embedded part is a "π" - shaped embedded part, as Figs. 1-2 shown.

[0081] S3, Construction of pier cap:

[0082] At the connection between the pier cap and the pier, the formwork fits tightly with the pier without any slurry leakage. The steel bars of the pier cap are welded to the embedded parts. When welding the steel bars of the pier cap, avoid bending at the joints of the steel bars. When casting the concrete of the pier cap, adopt a casting sequence of first casting the mid - span and then the cantilever, gradually approaching the fulcrum. Conduct two surface tamping on the concrete surface before the concrete initial - sets and carry out sprinkler maintenance.

[0083] S4, Backfill of pier:

[0084] When the strength of the pier concrete reaches 78%, backfill the pier backfill material to ensure the stability of the wall. The backfill soil of the pier is gravelly soil. Strictly control the layer thickness and compaction degree during the backfill of the pier. The maximum loose laying thickness of each layer of filling material is 20 cm. During compaction, do not let the wall body be affected by impact. Within a range of 1.0 m adjacent to the pier back, use small compaction tools such as a frog - type rammer, an internal combustion rammer or a hand - held vibrating roller for compaction. The compaction degree of the backfill soil of the pier is 97%.

[0085] S5, Installation of Bailey beam:

[0086] The Bailey beam is pre - assembled on land according to the design. Considering that the deflection of the Bailey beam mainly comes from the pulling and squeezing of the gaps between the pin holes, when installing the Bailey pins, use a large hammer to knock them manually so that the Bailey pins are tightly inserted into the pin holes and the safety pins are inserted to avoid leaving gaps. After the Bailey beam is assembled, it is directly hoisted in place by a crane. Install the upper and lower reinforcing chords of the Bailey truss. Use U - bolts to lock the Bailey beam and the longitudinal I - beam cross - beams on both sides to increase the overall stability and safety of the temporary bridge. After the Bailey beam is installed, install the I - beam transverse distribution beams, arranged at an interval of 30 cm. The transverse I - beams are locked to the Bailey beam using U - bolts.

[0087] A support flower frame is arranged inside the truss sheet group of the Bailey truss.

[0088] S6, bridge deck mounting:

[0089] The bridge deck is supported on reinforced Bailey beams and securely connected to the Bailey panels with U-bolts.

[0090] The bridge deck uses standard steel bridge deck and is fixed to Bailey beams with U-bolts; the bridge deck is equipped with drainage holes to ensure that water does not accumulate, and the water flow on both sides of the abutment is diverted into the river to avoid water accumulation on the bridge.

[0091] S7, Guardrail Installation:

[0092] After the bridge deck is installed, double I16 I-beams are welded on both sides of the lane to prevent the wheels from slipping off the bridge deck; the guardrail is made of 30*3mm square tubing, with a height of 1.3m, a vertical pole spacing of 1m, and a horizontal pole spacing of 0.4m.

[0093] Example 2

[0094] The steel trestle bridge is located at kilometer marker K33+200; the bridge is 28 meters long and 4.5 meters wide.

[0095] The construction method of the steel trestle bridge in this embodiment is the same as that in Embodiment 1, except that:

[0096] In S1.2, a C20 concrete cushion layer with a thickness of 12cm is poured on the base.

[0097] In S1.3, adding 3mm of rubber or sponge padding at the joints of the template effectively prevents grout leakage.

[0098] In S1.4, the concrete ridge is 10cm away from the edge of the enlarged base; the height of the concrete ridge is 5cm.

[0099] In S4, after the concrete strength of the abutment body reaches 80%, the backfill material is carried out; the maximum loose thickness of each layer of backfill is 18cm; the compaction degree of the backfill soil is 97%.

[0100] In S5, I-beam transverse distribution beams are installed, spaced 25cm apart.

[0101] In S7, the guardrail height is 1.4m, the spacing between uprights is 0.9m, and the spacing between horizontal bars is 0.4m.

[0102] Example 3

[0103] The steel trestle bridge is located at kilometer marker K33+300; the bridge is 25 meters long and 5 meters wide.

[0104] In S1.2, a C20 concrete cushion layer with a thickness of 11cm is poured on the base.

[0105] In S1.3, adding 2.5mm of rubber or sponge padding at the joints of the template can effectively prevent grout leakage.

[0106] In S1.4, the concrete ridge is 6cm away from the edge of the enlarged base; the height of the concrete ridge is 4cm.

[0107] In S4, after the concrete strength of the abutment body reaches 76%, backfill material is carried out; the maximum loose thickness of each layer of material is 16cm; the compaction degree of the backfill is 98.5%.

[0108] In S5, I-beam transverse distribution beams are installed, spaced 35cm apart.

[0109] In S7, the guardrail height is 1.5m, the spacing between uprights is 0.9m, and the spacing between horizontal bars is 0.5m.

[0110] Example 4

[0111] The steel trestle bridge is located at kilometer marker K26+700; the bridge is 12 meters long and 6 meters wide.

[0112] In S1.2, a C20 concrete cushion layer with a thickness of 12cm is poured on the base.

[0113] In S1.3, adding 3mm of rubber or sponge padding at the joints of the template effectively prevents grout leakage.

[0114] In S1.4, the concrete ridge is 8cm away from the edge of the enlarged base; the height of the concrete ridge is 5cm.

[0115] In S4, after the concrete strength of the abutment body reaches 79%, backfilling of the abutment backfill material is carried out; the maximum loose thickness of each layer of backfill material is 17cm; the compaction degree of the backfill soil is 98%.

[0116] In S5, I-beam transverse distribution beams are installed, spaced 33cm apart.

[0117] In S7, the guardrail height is 1.45m, the spacing between uprights is 0.9m, and the spacing between horizontal bars is 0.45m.

[0118] The superstructure of the steel trestle bridges in Examples 1-4 consists of 8mm patterned steel plates, I16 I-beams, and reinforced Bailey bridges with a spacing of 450mm. The cap is an L-shaped reinforced concrete wall with a concrete grade of C30. The pier body and enlarged foundation are made of C30 plain concrete.

[0119] Crane selection:

[0120] The installation is carried out using a "dual-machine lifting" method, with a maximum lifting capacity of 12 tons.

[0121] (1) The Bailey beam is operated using a dual-crane lifting system: Q_main + Q_auxiliary ≥ K(Q1 + Q2)

[0122] That is, Q1 = 12 tons. Considering the dynamic load factor of 1.4 and the weight of the rigging Q2 = 1 ton, that is: Q main + Q auxiliary ≥ 1.4 × (12 + 1) = 18.2 tons.

[0123] (2) Calculation of lifting height

[0124] H≥H1+H2+H3+H4

[0125] In the formula, H represents the lifting height of the crane (m) and the distance from the crane's stopping surface to the hook.

[0126] H1—Installation height (m);

[0127] H2 – Installation gap, which depends on the specific situation, and is generally 0.2-0.3m;

[0128] H3—Distance from the binding point to the bottom surface of the component after lifting (m);

[0129] H4 – Rigging height (m), the distance from the rigging point to the hook, depending on the specific situation.

[0130] Let H1 = 4 meters, H2 = 0.3 meters, H3 = 2 meters, and H4 = 1 meter. The lifting height of the selected crane should be H ≥ 7.3 meters, therefore, the lifting height is 7.3 meters.

[0131] (3) Calculation of crane boom length:

[0132] l≥(H+h0-h) / sinα

[0133] In the formula, l represents the length of the crane boom (m).

[0134] H—Lifting height (m);

[0135] h0——The distance from the top of the boom to the bottom of the hook (m), taken as 2m;

[0136] h——Distance from the bottom hinge of the crane boom to the stopping surface (m), taken as 1.5m;

[0137] α—Lifting boom elevation angle, generally taken as 30°~80°, and 60° is used in this project.

[0138] l≥(7.3+2-1.5) / sin60°)=6.75m.

[0139] (4) The maximum working radius of the crane is 15m. Referring to the lifting performance table of the 80-ton truck crane, we can get Q_main + Q_auxiliary ≥ Q1 + Q2, that is, 9.4 + 12.3 = 21.7 > 18.2t. Considering all of (1), (2), (3) and the working radius of the crane, one 80-ton truck crane is selected to cooperate with one 25-ton truck crane to meet the construction requirements.

[0140] The steel trestle bridges in Examples 1-4 were inspected and accepted. The heaviest vehicle to cross the temporary bridge was a crawler crane / dump truck. During the inspection, a truck fully loaded with cement (approximately 70 tons including the truck's own weight and the cement) crossed the temporary bridge, and displacement was observed at the abutments and mid-span. No displacement was observed. After 12 months of use, the steel trestle bridges did not exhibit any displacement, collapse, cracks, or fractures, demonstrating good resistance to harsh environments (seasonal changes, long winters and summers, drastic temperature variations, diurnal temperature differences, long hours of sunshine, large extreme temperature changes, snowmelt, rainfall, groundwater, etc.).

Claims

1. A construction method for a steel trestle bridge, characterized in that, The construction method includes the following steps: S1, Bridge abutment foundation construction: S1.1, Excavation of the foundation pit: The foundation pit shall be excavated by an excavator. When the foundation pit is excavated to 20cm from the base, manual excavation shall be used. Over-excavation is strictly prohibited. The excavation of the foundation pit shall not be interrupted. After the design elevation is reached and the inspection is qualified, the foundation shall be poured immediately. S1.2, Subbase pouring: Pour a C20 concrete subbase with a thickness of 10~12cm on the base, spread and level it, to protect the base and make the base surface flat, so as to facilitate the binding of steel bars and the installation of formwork. S1.3, Formwork installation: The joints between the formwork panels must be tight and leak-proof, with no steps. To ensure that the joints do not leak during construction, a 2-3mm rubber or sponge pad should be added to the joints of the formwork panels. S1.4, Enlarged Foundation Concrete Pouring: Concrete pouring shall be carried out using the "chute method" or "pumping method". During the concrete pouring process, the slump of the concrete shall be fully considered, and the free fall height of the concrete shall be controlled to be no more than 2m. If it exceeds 2m, a chute shall be used in conjunction with the pouring to avoid segregation. After the concrete is poured, the concrete surface shall be repaired and smoothed in a timely manner. After the concrete has hardened, a second smoothing shall be carried out. The joint of the abutment shall be roughened to expose the large particles of stone in the concrete to ensure a good connection between the abutment and the enlarged foundation concrete. Before pouring the concrete as described in each section, a precast concrete rib with an equilateral triangular cross section is placed at the edge of the enlarged foundation ring, with the concrete rib 5-10cm away from the edge of the enlarged foundation; the height of the concrete rib is 3-6cm, and the length of the concrete rib is equal to the width of the pouring surface. S2, Bridge abutment construction: S2.1, Construction Surveying; S2.2, Template Installation; S2.3, Abutment Concrete Pouring: The abutment body is constructed in layers, with each layer being 2m high; C30 concrete is used, and the concrete is poured in horizontal layers with a layer thickness not exceeding 30cm; the concrete is vibrated using an immersion vibrator, and the vibration time at each vibration point is 20-30s, until the concrete stops settling, no air bubbles appear, and laitance appears on the surface of the air bubbles. After the concrete is poured, the concrete surface is promptly repaired, smoothed, and leveled. After the concrete has hardened and set, a second smoothing is performed. The concrete is poured in layers until 60cm remains from the top of the platform. The embedded parts are then embedded in the concrete to facilitate the connection between the embedded parts and the reinforced concrete part of the platform cap. S3, abutment cap construction: At the connection between the cap and the body, the formwork and the body are tightly fitted to prevent grout leakage. The steel bars of the cap are welded to the embedded parts. When welding the steel bars of the cap, avoid bending at the joints of the steel bars. The concrete of the cap is poured in the following order: first pour the middle span, then the cantilever, and gradually move towards the support. Before the concrete sets, the surface of the concrete is finished twice and watered for curing. S4, Backfill behind the abutment: When the concrete strength of the abutment reaches 75% or more, backfill material is carried out to ensure the stability of the wall. The backfill material is gravelly soil. The backfill layer thickness and compaction are strictly controlled. The maximum loose thickness of each layer of material is no more than 20cm. During compaction, the wall should not be affected by impact. Within 1.0 meter of the back of the wall, a frog-type rammer, an internal combustion rammer, or a hand-held vibratory roller is used for compaction. The compaction degree of the backfill material is no less than 96%.

2. The construction method of a steel trestle bridge according to claim 1, characterized in that, In S1.1, drainage ditches and sump pits are set up around the foundation pit to pump out the water in the foundation pit in time to prevent the foundation pit and foundation from being soaked; in the foundation pit where surface water is flooded, cofferdams are built, rivers or ditches are changed, and dams are built to drain the surface water before excavation. When the bridge abutment is placed on the water surface, and the water depth exceeds 1.5m, the flow velocity is less than 0.5m / s, and the riverbed soil has low permeability and meets the flood discharge requirements, an earthen cofferdam should be constructed. Before constructing the earthen cofferdam, tree roots, stones, and other debris at the bottom of the riverbed should be removed. The cofferdam material should be cohesive soil or sand mixed with clay. Construction should begin from the upstream and end at the downstream closure point, and the surface should be compacted after it exceeds the water surface. If there is a risk of erosion on the outer slope of the cofferdam, erosion-resistant materials should be used for protection. When the bottom of the foundation pit is dry soil, each side of the foundation design plane should be widened by no less than 50cm, and vertical excavation should be carried out without formwork. When the bottom of the foundation pit is water-bearing soil, drainage ditches and collection wells shall be set up, with each side widened by no less than 80cm according to the foundation design plane dimensions; over-excavation of the foundation shall be avoided, and loose parts shall be removed; when using mechanical excavation, the structure of the foundation soil shall not be damaged, and a certain protective layer shall be retained 20cm above the design elevation, and then manual excavation shall be carried out. After the foundation is excavated, a bearing capacity test is conducted on the foundation. If the bearing capacity of the foundation is less than the design requirements, the foundation is replaced with filler. The replacement depth is not less than 50cm, and the treatment range extends more than 50cm beyond the bottom of the foundation. After the replacement is completed and compacted, the next construction procedure is carried out after the inspection is passed.

3. The construction method of a steel trestle bridge according to claim 1, characterized in that, In S1.3, the template uses customized steel templates, fastener-type steel pipe scaffolding, and is lifted by truck crane. The template surface is flat, smooth and not easily deformed. Before assembling the formwork, grind the surface of the formwork with a grinder, clean it, and apply a long-lasting release agent. Before pouring concrete, check the formwork's plane position, top elevation, joint connections, and longitudinal and transverse stability. Concrete can only be poured after confirmation.

4. The construction method of a steel trestle bridge according to claim 1, characterized in that, In S1.4, concrete is poured continuously. After each section of foundation concrete is poured once, the concrete is poured horizontally in layers within the entire flat section. The thickness of each layer is controlled within 30cm, and the longest interval is no more than the initial setting time of the concrete. The concrete is vibrated using an immersion vibrator. The distance between vibrator movements does not exceed 1.5 times the radius of action of the vibrator, and the vibrator is inserted 5-10cm into the lower layer. The vibration is uniform, and there should be no missed vibrations. The reinforcement and formwork should not be touched. The sign of compaction is that the concrete stops settling, no more air bubbles emerge, the surface is flat and covered with slurry, and the vibration time is 10-20s.

5. The construction method of a steel trestle bridge according to claim 1, characterized in that, The construction of bridge abutment foundations also includes S1.5, foundation curing: after the concrete strength reaches 2.5 MPa, the formwork is removed. After the concrete has initially set, it is covered with geotextile and watered for curing to ensure that the concrete surface is fully moist. When the ambient temperature is below 5℃, the concrete surface is insulated. Direct watering of the concrete is prohibited. The curing time shall not be less than 7 days.

6. The construction method of a steel trestle bridge according to claim 1, characterized in that, S2.1 The construction surveying method is as follows: mark each control point of the bridge abutment on the top surface of the foundation concrete, and use an ink line to mark the plane position of the bridge abutment. The ink line should extend beyond the template line so that the template can be corrected, scaffolding can be erected, guardrails and safety nets can be installed, and a working platform can be set up when installing the template. S2.2 The template installation method is as follows: Install the template at the position of the bridge abutment plane marked by the ink line on the top of the foundation concrete, adjust the top surface of the template to be level, and fill the gap between the bottom of the template and the foundation concrete with M10 mortar to prevent grout leakage when the abutment concrete is poured.

7. The construction method of a steel trestle bridge according to claim 1, characterized in that, Construction methods also include: S5, Bailey beam installation: The Bailey bridge beams are pre-assembled on land according to the design. Considering that the deflection of the Bailey bridge mainly comes from the tension and compression of the gaps between the pin holes, the Bailey pins are manually hammered with a large iron hammer during installation to ensure that the Bailey pins are tightly inserted into the pin holes, and safety pins are inserted to avoid leaving gaps. After the Bailey bridge beams are assembled, they are directly lifted into place by a crane, and the upper and lower reinforcing chords of the Bailey truss are installed. The Bailey bridge beams and the longitudinal I-beam crossbeams on both sides are locked with U-bolts to increase the overall stability and safety of the temporary bridge. After the Bailey bridge beams are installed, the transverse I-beam distribution beams are installed with a spacing of 30±5cm, and the transverse I-beams are locked to the Bailey bridge beams with U-bolts. The Bailey truss has supporting flower racks installed within the truss segments.

8. The construction method of a steel trestle bridge according to claim 7, characterized in that, Construction methods also include: S6, bridge deck mounting: The bridge deck is supported on reinforced Bailey beams and securely connected to the Bailey panels with U-bolts. The steel trestle bridge has a clear width of 4-6m. The bridge deck uses standard steel bridge deck and is fixed to Bailey beams with U-bolts. Drainage holes are set on the bridge deck to ensure that water does not accumulate. Water is diverted into the river from both sides of the abutment to avoid water accumulation on the bridge.

9. A construction method for a steel trestle bridge according to claim 8, characterized in that, Construction methods also include: S7, Guardrail Installation: After the bridge deck is installed, double I16 I-beams are welded on both sides of the lane to prevent the wheels from slipping off the bridge deck; the guardrails are made of 30*3mm square tubes, with a height of 1.3~1.5m, a vertical pole spacing of 0.8~1m, and a horizontal pole spacing of 0.4~0.5m.

10. A construction method for a steel trestle bridge according to claim 1, characterized in that, In S2.3, the embedded part is a "π"-shaped embedded part.

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