Construction method for replacing existing prefabricated floor slab with cast-in-place floor slab after dismantling

Abstract

A construction method for replacing an existing prefabricated floor slab with a cast-in-place floor slab after dismantling comprises the steps that when an original prefabricated slab is dismantled in a blocking mode, guide holes are drilled in a wall body within the height range of the original prefabricated slab, an outer wall connecting steel beam and an inner wall connecting diagonal bracing steel beam are installed in the corresponding guide holes, and fine aggregate concrete is poured to compact the guide holes; the inner wall connection diagonal bracing type steel beams are mutually used for connecting the cast-in-place reinforced concrete floors of every two adjacent rooms in series; the opposite-penetrating type steel beams serve as stable lateral supports of the wall body after the prefabricated floor slab is dismantled. The opposite-penetrating type steel beams are left in the replaced cast-in-place slab and serve as force transmission pieces of the cast-in-place slab and the masonry wall and connecting pieces of adjacent room floor slabs. After the original prefabricated slabs are removed and the steel beams are fixed, formwork erecting, reinforcing mesh laying and concrete pouring are completed; and after concrete curing is completed, the formwork is disassembled. According to the construction method, on the premise that an original masonry bearing wall is reserved, an original prefabricated slab is replaced with a cast-in-place reinforced concrete floor after being dismantled.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of floor reconstruction construction, and in particular to a construction method for replacing a precast floor with a cast-in-place floor after the precast floor is removed. BACKGROUND

[0002] With the development of social economy, the state encourages the protection and renewal of existing buildings in urban and rural areas from a policy perspective, to avoid the disappearance of the original memory of the city caused by large-scale demolition and construction. Brick masonry structure buildings built in different years, which inherit the Chinese Qin brick and Han tile tradition, need to be preserved. Due to the technical conditions at the time of construction, the floor panels of these brick wall houses are mostly precast concrete panels or wooden purlin floors, which have poor integrity and cannot meet the functional requirements of the reconstruction and utilization. Therefore, it is necessary to perform functional reconstruction of the interior of the house while preserving the original architectural style, and an important part of the reconstruction is structural reinforcement and seismic reinforcement.

[0003] Precast concrete channel panels and hollow core panels are commonly used precast components for floor panels of existing brick wall houses. The channel panel has a cross-section in the shape of a downwardly open groove, with ribbed beams on both sides and a thin panel in the middle. The hollow core panel usually has a hollow circular hole in the panel. The precast floor panels of the original masonry structure have low bearing capacity and poor integrity, and therefore need to be replaced with cast-in-place panels during reconstruction. The technical difficulty is that the original precast panels are placed in the brick wall, and the removal of the precast panels will cause the wall to lose lateral support, resulting in instability. The newly added cast-in-place panels cannot be simply embedded in the original wall. For the above reasons, a reliable technology is needed to safely remove the precast floor panels of the masonry structure and replace them with cast-in-place floor panels in engineering practice. SUMMARY

[0004] The present application aims to solve the problems existing in the prior art, and provides a construction method for replacing a precast floor with a cast-in-place floor after the precast floor is removed. The construction method for replacing a precast floor with a cast-in-place floor after the precast floor is removed replaces the original precast panels of an existing building with cast-in-place reinforced concrete floor panels under the premise of preserving the original masonry bearing wall, and the cast-in-place reinforced concrete floor panels replace the original precast panels without the need to remove the original masonry bearing wall and then cast.

[0005] The present application is implemented by using the following technical solutions: A construction method for replacing a precast floor with a cast-in-place floor after the precast floor is removed, comprising the following steps: A. Preparing outer wall connecting steel beams and inner wall connecting bracing steel beams according to the size of the room and the design.

[0006] B. Removing the original precast panels in blocks, and drilling inner wall steel beam installation guide holes in the original masonry bearing inner walls within the height range of the original precast panels, and drilling outer wall steel beam installation guide holes in the original masonry bearing outer walls.

[0007] C. Install the exterior wall connection steel beams and interior wall connection bracing steel beams in the interior wall steel beam installation guide holes and the exterior wall steel beam installation guide holes respectively. After the steel beams are installed, pour C30 fine stone concrete to compact the guide holes. The interior wall connection bracing steel beams penetrate the original masonry load-bearing interior walls to connect the cast-in-place reinforced concrete floor slabs of each two adjacent rooms in series. At least one interior wall connection bracing steel beam is laid at the location of each original precast panel. One end of the exterior wall connection steel beam is fixed in the original masonry load-bearing exterior wall, and the other end of the exterior wall connection steel beam penetrates the adjacent original masonry load-bearing interior wall to connect the cast-in-place reinforced concrete floor slabs of two adjacent rooms in series. At least one exterior wall connection steel beam is laid at the location of each original precast panel. Repeat the above steps for each original precast panel removed. The bracing steel beams serve as lateral supports for the stability of the wall after the precast floor slabs are removed. The bracing steel beams are left in the replaced cast-in-place slabs to serve as force transmission members between the cast-in-place slabs and masonry walls and as connectors for the floor slabs of adjacent rooms.

[0008] D. After the existing precast panels in the same room are removed and the steel beams are secured, the formwork for the cast-in-place reinforced concrete floor slabs is erected. The steel mesh for the cast-in-place reinforced concrete floor slabs is laid on the steel beams, and then concrete is poured. Each room corresponds to a replacement cast-in-place reinforced concrete floor slab. After the original precast panels are removed, the stability of the masonry walls is ensured by using exterior wall connecting steel beams and interior wall connecting bracing steel beams. This ensures a reliable connection between the original load-bearing masonry exterior and interior masonry walls and the replaced cast-in-place reinforced concrete floor slabs. The replacement sequence for cast-in-place reinforced concrete floor slabs is completed floor by floor, from bottom to top. The cast-in-place reinforced concrete floor slabs of adjacent rooms are connected by interior wall connecting bracing steel beams to form a single unit. The exterior wall connecting steel beams and interior wall connecting bracing steel beams are embedded in the newly replaced cast-in-place reinforced concrete floor slabs as shear members that transmit the floor slab's gravity load to the walls, greatly enhancing the floor slab's integrity and seismic performance.

[0009] E. After the concrete curing is completed, the formwork can be removed.

[0010] Further preferably, the outer wall connecting steel beams and the inner wall connecting bracing steel beams are arranged alternately at intervals.

[0011] Further preferred: before erecting the formwork for the cast-in-place reinforced concrete floor slab, a steel mesh concrete reinforcement layer is tightly installed on the inner side of the original masonry load-bearing exterior wall and on both sides of the original masonry load-bearing interior wall, and the formwork for the cast-in-place reinforced concrete floor slab is erected to ensure that the top surface of the formwork is not higher than the top surface of the steel mesh concrete reinforcement layer, so that the cast-in-place reinforced concrete floor slab is connected to the top of the steel mesh concrete reinforcement layer, and the cast-in-place reinforced concrete floor slab is used in combination with the composite wall reinforced by the steel mesh concrete reinforcement layer to achieve reinforcement of the component bearing capacity and seismic performance of the masonry wall structure.

[0012] Further preferred: when the exterior wall is connected to the steel beam, the end of the exterior wall connecting steel beam inserted into the exterior wall steel beam installation guide hole is connected to the anchor, the anchor includes an anchor plate and an anchor bar, the anchor plate is attached to the outside of the original masonry load-bearing exterior wall, one end of the anchor bar is fixedly connected to the anchor plate, and before pouring the C30 fine stone concrete to fill the hole, the other end of the anchor bar is passed through the original masonry load-bearing exterior wall and welded to the exterior wall connecting steel beam.

[0013] This construction method of replacing existing prefabricated floor slabs with cast-in-place floor slabs after demolition retains the original masonry load-bearing walls. The original prefabricated panels of the existing building are demolished and replaced with cast-in-place reinforced concrete floor slabs. The cast-in-place reinforced concrete floor slabs replace the original prefabricated panels, and there is no need to demolish the original masonry load-bearing walls before casting. During construction, the original prefabricated panels are demolished block by block. While demolishing the original prefabricated panels block by block, inner wall steel beam installation guide holes are drilled on the original masonry load-bearing inner walls within the height range of the original prefabricated panels, and outer wall steel beam installation guide holes are drilled on the original masonry load-bearing outer walls. Install the exterior wall connection steel beams and interior wall connection bracing steel beams in the interior wall steel beam installation guide holes and the exterior wall steel beam installation guide holes accordingly. After the steel beams are installed, pour C30 fine stone concrete to fill the guide holes densely. The interior wall connection bracing steel beams penetrate the original masonry load-bearing interior walls to connect the cast-in-place reinforced concrete floor slabs of each two adjacent rooms in series. At least one interior wall connection bracing steel beam is laid at the location of each original precast panel. One end of the exterior wall connection steel beam is fixed in the original masonry load-bearing exterior wall, and the other end of the exterior wall connection steel beam penetrates the adjacent original masonry load-bearing interior wall to connect the cast-in-place reinforced concrete floor slabs of two adjacent rooms in series. At least one exterior wall connection steel beam is laid at the location of each original precast panel. Repeat the above steps for each original precast panel removed. Steel beams are used to replace the lateral force transmission of the original precast panels to ensure the stability of the wall. The exterior wall connecting steel beams and the interior wall connecting bracing steel beams are embedded in the newly replaced cast-in-place reinforced concrete floor slabs as shear members that transmit the floor slab gravity load to the wall, greatly increasing the integrity and seismic performance of the floor slabs. A steel mesh concrete reinforcement layer is set closely on the original wall, and the cast-in-place reinforced concrete floor slab is connected to the top of the steel mesh concrete reinforcement layer. The cast-in-place reinforced concrete floor slab is combined with the composite wall reinforced by the steel mesh concrete reinforcement layer to realize the reinforcement of the component bearing capacity and seismic performance of the masonry wall structure, so that the original masonry load-bearing wall does not need to be demolished and then cast, and the original masonry load-bearing wall is retained. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic cross-sectional view of a cast-in-place reinforced concrete floor slab; Figure 2 for Figure 1 Schematic diagram of the top view structure; Figure 3 This is a top view schematic diagram of the positional relationship between the steel beam and the original precast slab; The component names corresponding to the serial numbers in the figure are: 1. Original masonry load-bearing exterior wall, 2. Pilot holes for installing exterior wall steel beams, 3. Exterior wall connecting steel beams, 4. Original precast panels, 5. Original masonry load-bearing interior wall, 6. Interior wall connecting bracing steel beams, 7. Pilot holes for installing interior wall steel beams, 8. Cast-in-place reinforced concrete floor slabs, 9. Steel mesh concrete reinforcement layer, 10. Anchor plates, 11. Anchor bars. DETAILED DESCRIPTION

[0015] The technical solutions of the invention are clearly and completely described below in conjunction with the embodiments. The described embodiments are only a part of the present invention, rather than all the embodiments.

[0016] Example 1

[0017] The following steps can be used to complete the construction of replacing the existing precast floor slab with a cast-in-place floor slab after removal: A. Prepare the exterior wall connecting steel beams 3 and the interior wall connecting bracing steel beams 6 according to the room and design dimensions.

[0018] B. Dismantle the original prefabricated panels 4 in blocks. While dismantling the original prefabricated panels 4 in blocks, drill guide holes 7 for installing the inner wall steel beams on the original masonry load-bearing inner wall 5 within the height range of the original prefabricated panels 4, and drill guide holes 2 for installing the outer wall steel beams on the original masonry load-bearing outer wall 1.

[0019] C. Install exterior wall connecting steel beams 3 and interior wall connecting bracing steel beams 6 in the interior wall steel beam installation guide holes 7 and exterior wall steel beam installation guide holes 2, respectively. After the steel beams are installed, cast C30 fine stone concrete to compact the guide holes. The interior wall connecting bracing steel beams 6 penetrate the original masonry load-bearing interior wall 5 to connect the cast-in-place reinforced concrete floor slabs 8 of each adjacent room in series. At least one interior wall connecting bracing steel beam 6 is installed at the location of each existing precast panel 4. One end of the exterior wall connecting steel beam 3 is fixed in the original masonry load-bearing exterior wall 1, and the other end penetrates the adjacent original masonry load-bearing interior wall 5 to connect the cast-in-place reinforced concrete floor slabs 8 of each adjacent room in series. At least one exterior wall connecting steel beam 3 is installed at the location of each existing precast panel 4. The exterior wall connecting steel beams 3 and interior wall connecting bracing steel beams 6 are arranged alternately. Repeat the above steps for each existing precast panel 4 removed.

[0020] D. After the original precast panels 4 in the same room are removed and the steel beams are fixed, the formwork for the cast-in-place reinforced concrete floor slab 8 is erected, the steel mesh for the cast-in-place reinforced concrete floor slab 8 is laid on the steel beams, and then concrete is poured. Each room corresponds to a replaced cast-in-place reinforced concrete floor slab 8. After the original precast panels 4 are removed, the stability of the masonry walls is ensured by the exterior wall connecting steel beams 3 and the interior wall connecting bracing steel beams 6, so that the original masonry load-bearing exterior wall 1 and the original masonry load-bearing interior wall 5 are reliably tied to the replaced cast-in-place reinforced concrete floor slab 8. The replacement sequence of the cast-in-place reinforced concrete floor slab 8 is from bottom to top, layer by layer. The cast-in-place reinforced concrete floor slabs 8 of adjacent rooms are connected to form a whole by the interior wall connecting bracing steel beams 6. The exterior wall connecting steel beams 3 and the interior wall connecting bracing steel beams 6 are pre-embedded in the newly replaced cast-in-place reinforced concrete floor slab 8 as shear members that transmit the floor slab's gravity load to the wall, greatly increasing the integrity and seismic performance of the floor panel.

[0021] E. After the concrete curing is completed, the formwork can be removed.

[0022] Example 2

[0023] A. Prepare the exterior wall connecting steel beams 3 and the interior wall connecting bracing steel beams 6 according to the room and design dimensions.

[0024] B. Dismantle the original prefabricated panels 4 in blocks. While dismantling the original prefabricated panels 4 in blocks, drill guide holes 7 for installing the inner wall steel beams on the original masonry load-bearing inner wall 5 within the height range of the original prefabricated panels 4, and drill guide holes 2 for installing the outer wall steel beams on the original masonry load-bearing outer wall 1.

[0025] C. Install exterior wall connecting steel beams 3 and interior wall connecting bracing steel beams 6 in the interior wall steel beam installation guide holes 7 and exterior wall steel beam installation guide holes 2, respectively. After the steel beams are installed, cast C30 fine stone concrete to compact the guide holes. The interior wall connecting bracing steel beams 6 penetrate the original masonry load-bearing interior wall 5 to connect the cast-in-place reinforced concrete floor slabs 8 of each adjacent room in series. At least one interior wall connecting bracing steel beam 6 is installed at the location of each existing precast panel 4. One end of the exterior wall connecting steel beam 3 is fixed in the original masonry load-bearing exterior wall 1, and the other end penetrates the adjacent original masonry load-bearing interior wall 5 to connect the cast-in-place reinforced concrete floor slabs 8 of each adjacent room in series. At least one exterior wall connecting steel beam 3 is installed at the location of each existing precast panel 4. The exterior wall connecting steel beams 3 and interior wall connecting bracing steel beams 6 are arranged alternately. Repeat the above steps for each existing precast panel 4 removed. When the exterior wall connecting steel beam 3 is connected, the end of the exterior wall connecting steel beam 3 inserted into the exterior wall steel beam installation guide hole 2 is connected to the anchor. The anchor includes an anchor plate 10 and an anchor bar 11. The anchor plate 10 is attached to the outside of the original masonry load-bearing exterior wall 1. One end of the anchor bar 11 is fixedly connected to the anchor plate 10. Before pouring the C30 fine stone concrete to fill the hole, the other end of the anchor bar 11 is passed through the original masonry load-bearing exterior wall 1 and welded to the exterior wall connecting steel beam 3.

[0026] D. After the original precast panels 4 in the same room are removed and the steel beams are secured, the formwork for the cast-in-place reinforced concrete floor slab 8 is erected. The steel mesh for the cast-in-place reinforced concrete floor slab 8 is laid on the steel beams, and then concrete is poured. Each room corresponds to a replacement cast-in-place reinforced concrete floor slab 8. Before erecting the formwork for the cast-in-place reinforced concrete floor slab 8, a steel mesh concrete reinforcement layer 9 is installed on the inner side of the original masonry load-bearing exterior wall 1 and on both sides of the original masonry load-bearing interior wall 5. The formwork for the cast-in-place reinforced concrete floor slab 8 is erected to ensure that the top surface of the formwork is no higher than the top surface of the steel mesh concrete reinforcement layer 9. The cast-in-place reinforced concrete floor slab 8 is connected to the top of the steel mesh concrete reinforcement layer 9. The cast-in-place reinforced concrete floor slab 8 is used in combination with the composite wall reinforced by the steel mesh concrete reinforcement layer 9 to strengthen the bearing capacity and seismic performance of the masonry wall structure. After the original precast panels 4 are removed, the stability of the masonry walls is ensured by connecting the exterior wall steel beams 3 and the interior wall bracing steel beams 6, ensuring a reliable connection between the original load-bearing exterior masonry walls 1 and the original load-bearing interior masonry walls 5 and the replaced cast-in-place reinforced concrete floor slabs 8. The replacement sequence of the cast-in-place reinforced concrete floor slabs 8 is completed from bottom to top, floor by floor. The cast-in-place reinforced concrete floor slabs 8 of adjacent rooms are connected to form a whole by connecting the interior wall bracing steel beams 6. The exterior wall connecting steel beams 3 and the interior wall connecting bracing steel beams 6 are embedded in the newly replaced cast-in-place reinforced concrete floor slabs 8 as shear members that transmit the floor slab's gravity load to the wall, greatly enhancing the integrity and seismic performance of the floor slab.

[0027] E. After the concrete curing is completed, the formwork can be removed.

[0028] The precast concrete hollow core slabs placed on the brick wall are removed and replaced with cast-in-place concrete slabs. The steel sections (H-shaped steel, channel steel) replaced piece by piece provide lateral stability support for the masonry wall after the precast hollow core slabs are removed. The steel beams are left in the cast-in-place concrete slabs after replacement to transfer gravity loads to the masonry wall. The bearing capacity calculation is based on the following standards: 1. GB50010-2010 Code for Design of Concrete Structures, Shear Capacity of Oblique Sections of Rectangular Members, Article 6.3.3 of the Code for Design of Concrete Structures.

[0029] 2. Steel structure design standard GB50017-2017, shear bearing capacity of solid steel members, steel structure design standard Article 6.1.3.

[0030] Calculation of steel shear capacity for precast hollow core slab replacement, component specifications and material design parameters: L-span of a single corrugated plate (mm); B-width of a single corrugated plate (mm); H-height of a single corrugated plate (mm); h-height of the replacement steel (mm); t-thickness of the web of the replacement steel (mm); fv-design value of the shear strength of the replacement steel (N / mm2).

[0031] Force transmission of the original precast hollow-core slab: Precast hollow-core slabs or precast trough slabs transfer gravity loads to masonry walls through rib beams between the holes in the slabs. They can be equivalent to I-section beams or T-section beams. The design shear bearing capacity is borne by the rib beam concrete V=0.7ftbh0 (b is the total width of the concrete rib beams), and V<0.25fcbh0 is satisfied.

[0032] Shear capacity of steel sections after replacement: Each precast slab transfers gravity loads to the masonry wall via two interpenetrating steel beams. Generally, the weight of the cast-in-place slab after replacement is greater than that of the precast slab, so only the load transfer of the cast-in-place concrete slab after replacement needs to be calculated. V represents the vertical shear capacity of the steel sections, as determined by Article 6.1.3 of the Steel Structure Design Standard: VS / (It)=fv, so V=Itfv / S; To simplify the calculation for safety reasons, ignore the flange and only calculate the web: I=thhh / 12, S=thh / 8, V=Itfv / S=tfv(thhh / 12) / (thh / 8)=2thfv / 3.

[0033] Application example, component specifications and material design parameters: L-span of a single grooved plate 3600mm; B-width of a single grooved plate 800mm; H-height of a single grooved plate 110mm; h-height of the replacement steel 80mm; t-web thickness of the replacement steel 5mm; fv-design value of shear strength of the replacement steel (Q235 steel) 125N / mm2.

[0034] Monolithic slot type plate internal force calculation: considering the plate surface decoration layer 50mm, the plate bottom plastering 20mm, the plate thickness 100mm, according to the 25kN / m3 capacity, design dead load: q=(0.020+0.050)x0.8x25+0.1x0.8x25=1.4+2.0=3.4kN / m; Design live load 3.0kN / m2;P=3.0x0.8=2.4kN / m; Internal force design value requirement, V0=(1.3q+1.5p) / 2=(1.3x 3.4+1.5x2.4)x3.6 / 2=14.436kN.

[0035] Substitute steel shear capacity: select No. 8 channel steel, partial safety simplified calculation, do not count the wing plate, only calculate the web shear, I=thhh / 12, S=thh / 8;V=Itfv / S=tfv(thhh / 12) / (thh / 8)=2thfv / 3; Single channel steel V1=2x5x80x125 / 3=33333N=33.33kN; Each prefabricated plate is replaced by a beam root channel steel, and the shear capacity of the channel steel is V=2V1=66.66kN>V0, which meets the force transmission requirements of the cast-in-place plate.

[0036] The above description is not a limitation of the present application, and the present application is not limited to the above examples. Within the scope of the present application, changes, modifications, additions or substitutions made by ordinary skilled in the art should be within the scope of the present application.

Claims

1. A construction method for dismantling an existing prefabricated floor slab and replacing it with a cast-in-place floor slab, characterized by: The following steps are involved: A. Prepare the exterior wall connecting steel beams (3) and the interior wall connecting bracing steel beams (6) according to the room and design dimensions; B. Dismantle the original prefabricated panels (4) in blocks. While dismantling the original prefabricated panels (4) in blocks, drill guide holes (7) for installing the inner wall steel beams on the original masonry load-bearing inner wall (5) within the height range of the original prefabricated panels (4), and drill guide holes (2) for installing the outer wall steel beams on the original masonry load-bearing outer wall (1); C. Install the outer wall connection steel beam (3) and the inner wall connection bracing steel beam (6) in the inner wall steel beam installation guide hole (7) and the outer wall steel beam installation guide hole (2) respectively. After the steel beam is installed, pour C30 fine stone concrete to compact the guide hole. The inner wall connection bracing steel beam (6) penetrates the original masonry load-bearing inner wall (5) to connect the cast-in-place reinforced concrete floor slabs (8) of each two adjacent rooms in series. One end of the outer wall connection steel beam (3) is fixed in the original masonry load-bearing outer wall (1), and the other end of the outer wall connection steel beam (3) penetrates the adjacent original masonry load-bearing inner wall (5) to connect the cast-in-place reinforced concrete floor slabs (8) of the two adjacent rooms in series. Repeat the above steps for each original prefabricated panel (4) removed. D. After the original prefabricated panels (4) in the same room are removed and the steel beams are fixed, the formwork for the cast-in-place reinforced concrete floor (8) is erected, the steel mesh for the cast-in-place reinforced concrete floor (8) is laid on the steel beams, and then the concrete is poured; E. After the concrete curing is completed, the formwork can be removed.

2. The construction method for dismantling an existing prefabricated floor slab and replacing it with a cast-in-place floor slab according to claim 1, characterized in that: The outer wall connection steel beams (3) and the inner wall connection bracing steel beams (6) are arranged alternately at intervals.

3. The construction method for replacing existing prefabricated floor slabs with cast-in-place floor slabs after demolition according to claim 1 is characterized in that: Before setting up the formwork for the cast-in-place reinforced concrete floor slab (8), a steel mesh concrete reinforcement layer (9) is set up on both sides of the original masonry load-bearing outer wall (1) and the original masonry load-bearing inner wall (5), respectively. The formwork for the cast-in-place reinforced concrete floor slab (8) is set up to ensure that the top surface of the formwork is not higher than the top surface of the steel mesh concrete reinforcement layer (9), so that the cast-in-place reinforced concrete floor slab (8) is connected to the top of the steel mesh concrete reinforcement layer (9).

4. The construction method for dismantling an existing prefabricated floor slab and replacing it with a cast-in-place floor slab according to claim 1, characterized in that: When the external wall connecting steel beam (3) is connected, the end of the external wall connecting steel beam (3) inserted into the external wall steel beam installation guide hole (2) is connected to the anchoring piece, wherein the anchoring piece comprises an anchor plate (10) and an anchor bar (11), the anchor plate (10) is attached to the outside of the original masonry load-bearing external wall (1), one end of the anchor bar (11) is fixedly connected to the anchor plate (10), and before pouring the C30 fine stone concrete to fill the hole, the other end of the anchor bar (11) is passed through the original masonry load-bearing external wall (1) and welded to the external wall connecting steel beam (3).

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