CN1239796C - Building structural element - Google Patents

Abstract

A building structural element (1) having a pair of beams (5) joined by a plate member (13) or alternatively a generally U-shaped channel having a pair of opposed side walls (33, 34) joined by a further portion (35). In either case an interior space (57) is defined by either the pair of beams (5) and plate member (13) or by the pair of side walls (33, 34) and the further portion (35). A cementitious material, such as concrete, occupies a substantial volume of the interior space (57) and the building structural element (1) has a post-tensioned pre-stressing force applied thereto.

Description

Structural components of buildings and methods of making the same

technical field

The invention relates to a structural element of a building and a method of making a structural element of a building. More particularly, the present invention relates to structural elements for use in buildings within building floor systems and methods of making such elements.

The invention can also be used in many other construction applications, eg roof coverings over road tunnels, railway tracks and the like. It can be used for large multi-span floor spaces, especially with high floor-to-story dimensions, and/or large spans in one or two directions, and/or on floors such as those used for retail, entertainment, or other uses. Floor spaces with high floor loads. It can also be used for bridge decks and large spans and/or any other application where high loads must be carried between supports.

A particular aspect of the invention relates to floor beams for use in the construction of building floor systems and is preferably made from an assembly of two components, preferably steel and a cementitious material such as concrete .

Background technique

Beams are usually required for floor slab systems in buildings spanning more than 8 to 10 metres. The above spans are generally upper bounds or limits on how far a floor can be extended for structural support without the use of beams. The support columns are usually spaced 6 to 9 meters apart, with a common spacing of 8.4 meters. This is a suitable module for an office building that accommodates one column plus the width of three spaces that can be used for vehicle parking between two adjacent columns and can be used as the building's office floor (or retail any parking level below the commercial floor, institutional floor, or other floor). Beams are required to span the larger dimension of a rectangular floor between a grid of four columns or between a building and a pair of outer columns outside the core or central portion of a multistory building. The core is typically used to accommodate elevator shafts and other public spaces accessible to people on all levels. The slab system spanning these beams can and does take many forms, depending on site availability, economics, and the preferences of the owner, engineer, or builder, or a combination of the preferences of any of these three parties .

Floor system spanning about 8 meters in one direction between supporting beams in various variations: concrete slabs formed on conventional formwork or large platform forms, concrete slabs on metal brackets , these metal brackets are temporarily supported on supported, near-centre (2.1 to 3.0 m) steel secondary beams that support relatively thin slabs on unsupported metal bracket formwork. There are also other specialized systems such as various prestressed slab systems which can span unsupported distances of 7 to 8 meters.

For supporting beams, the upper range suitable for reinforced concrete shallow hooped beams is about 10 to 12 meters. For prestressed shallow hooped beams (usually post-tensioned), the upper limit of applicability is usually in the range of 12 to 14 metres. However, for spans longer than 12 to 14 metres, special attention and attention to detail are required and common solutions are steel or prestressed concrete floor beams.

In a steel floor beam system, there are a series of steel beams spaced 2.1 to 3.0 meters on center that span the larger distances of a rectangular floor plan and are supported by 'main' beams that span the shorter distances between supporting columns. A particular problem faced by most engineers or designers is the need to reduce the amount of deflection of each beam due to dead or live loads, or a combination of the two, in systems using floor beams. Unnecessarily large deflections and vibrations of the floor system can affect the suitability of the floor.

A disadvantage of the currently used steel floor beam systems is that the individual beams require strong connections at their supports. Beams and joints often require a protective coating to make them fire resistant. Although such steel floor beams can be made to function in combination with relatively thin slabs supported by shear studs, there is a small, small amount of static deflection due to creep at the concrete and shear stud interface. Evolving heft. Most of the deflection of the steel beam caused by the static load occurs as soon as the load is applied, and can be offset by the pre-arching of the beam. However, deflection and vibration due to transient live loads remain an inherent problem, especially for longer-span beams, since composite steel beams are stiffer than those used for reinforced or prestressed concrete beams of the same span The stiffness is small.

Other types of floor beam systems in general use today are post-tensioned, prestressed concrete floor beam systems. They include concrete beams with a deep aspect ratio, in other words concrete beams sized such that their height is greater than their width, and for beams spanning over 10 metres, these concrete beams are usually prestressed. The concrete beams and the slabs they support are cast in situ. Prestressing is then achieved by post-tensioning tendons that apply stress when the concrete has reached sufficient strength, usually within 3 to 6 days of pouring. Concrete beams and adjacent slabs are usually formed on large deck forms that are lifted from one slab to the other by cranes. Two sets of platforms are usually used to maintain a good cycle of the slab for about one week, and to provide continuity of work for various other operations while pouring half of the slab area. Apart from the reinforced skeleton of the beams (which may or may not include prestressing reinforcement), there is little possibility of prefabrication. Any prefabricated steel skeleton needs to be well braced and resting on supports so that it can be hoisted into the beam formwork by a crane. In general, when concrete joins beams to support columns, there are no difficult connections at the supports of the beams. When a cast-in-place concrete beam is supported on a concrete core that has been "jump formed" before the main floor slab, the connection can be a simple tenon and tenon in the walls of the concrete core, with reinforcement at the top and bottom of the beam Screwed into hoops anchored in the concrete core. Alternatively, the beams may sit in pockets left in the concrete core.

Prestressed concrete floor systems are stiffer than steel floor beam systems required to span the same distance and are therefore less prone to floor vibration and deflection due to transient loads. However, when the concrete creeps under sustained load, the deflection of the slab system increases after the slab is occupied, not only because of live loads and light partitions, but also because the creep component is significantly increased by static loads. deflection share. Prestressing balances most of the deflection due to static loads only. However, since the axial prestress imparts a permanent axial force to the beam, the shortening over time causes a loss of the prestress, which leads to further increased deflection of the beam.

Contents of the invention

It is an object of the present invention to provide a structural element of a building which substantially overcomes one or more of the aforementioned disadvantages. Specifically, the present invention provides a structural member of a building that has minimal deflection and substantially maintains axial prestress therein and reduces axial creep due to beam shortening as in prior art systems. The loss of this prestress caused by the change.

According to a first aspect of the present invention there is provided a structural element of a building comprising:

a pair of beams, each beam in the pair having a first flange portion, a second flange portion, and a flange extending between the first flange portion and the second flange portion the web part;

a plate adapted to engage with one of said first flange portion or said second flange portion of each beam such that a an internal space;

Wherein, the cement-like material occupies the main volume of the interior space to form a non-integral building structural member, and after post-tensioning prestress is applied, under static load, the structural member of the building With residual deflection or no deflection.

The structural members of the building may also include one or more steel bars extending the length of the interior space formed between the beams and the panels which may be metal bracket form soffits. Each of the one or more bars may be prestressed to provide an upwardly directed force which counteracts a portion of the dead load. The first flange portion of each beam may support a portion of the floor span after the structural member is secured at each end. Generally, structural members may extend between a column and the core of a building. Structural members may terminate at a short distance from the core and a short distance from the columns, or at each end a short distance from a column, and be temporarily supported at their ends, and possibly also at mid-span on scaffolding.

The beams are preferably constructed of metal such as steel and the cementitious material is preferably concrete.

According to a second aspect of the present invention, there is provided a structural member of a building comprising:

a pair of beams, each beam in the pair having a top flange portion, a bottom flange portion, and a web portion extending between the top flange portion and the bottom flange portion ;

a plate adapted to engage a corresponding bottom flange portion of each of said pair of beams such that an interior space is formed within each of said pair of beams and said plate;

Wherein, the cementitious material occupies the main volume of the inner space to form a non-integral building structural member, and after applying post-tension prestress, the structural member of the building has residual deflection or no deflection.

The panels may be metal bracket form soffits, or other suitable horizontal soffit surfaces.

According to a third aspect of the present invention, there is provided a structural member of a building comprising:

a generally U-shaped trough means having a pair of opposing side walls and another portion connecting the side walls;

wherein the pair of opposite side walls and the other portion form an interior space; and

wherein the cementitious material occupies the main volume of said interior space to form a non-integral building structural element within the trough device, said building being under static load after application of a post-tensioned prestress of structural members have residual deflection or no deflection.

According to a fourth aspect of the present invention, there is provided a method of making a building structural member, which includes the following steps:

constructing a pair of beams, each beam in the pair comprising a first flange portion, a second flange portion, and extending between the first flange portion and the second flange portion a web portion of;

forming and assembling a panel so that the panel engages one of said first flange portion or said second flange portion of each beam such that an internal space; and

pouring cementitious material into said interior space to form a non-integral building structural member such that, after said cementitious material has hardened and post-tensioned prestressed, said building The structural members of the object are basically deflection-free.

The pouring step may be performed separately, or as part of pouring the adjacent floor spans supported by the structural member. Structural members may utilize possible additional support along the span with their ends initially supported on temporary support structures adjacent to the permanent end supports of the beams.

Description of drawings

Preferred embodiments of the present invention will be described below by way of example with reference to the accompanying drawings, in which:

1 is a plan view of a portion of a building floor system extending between a core wall of a building and an edge of the building;

FIG. 2 is exploded into FIGS. 2A and 2B and is a side sectional view taken along line A-A of FIG. 1;

Figure 3 is a cross-sectional view of a structural member in use according to an embodiment of the present invention, taken along line B-B of Figure 2;

Figure 4 is a cross-sectional view of the structural member in use, taken along line C-C of Figure 2;

Figure 5 is a cross-sectional view of a structural member in use similar to Figure 3 and according to another embodiment;

Figures 5(a) to 5(d) are side views of the structural member in Figure 5, showing individual instances of the structural member;

Figure 6 is a cross-sectional view similar to Figure 4 of another embodiment of a structural member in use;

7 is a side sectional view showing a structural member applied to a tunnel cover;

Figure 8 is a side view of a prior art prefabricated structural member; and

Figure 9 shows a plan view and a side view of a structural member across a floor span with secondary support beams.

Detailed ways

Figure 1 shows a plan view of a pair of structural members 1, each extending from side columns 2 on an outer edge of a building to a core wall 3 in the central part of the building. The span of each structural member can extend up to and beyond 18 meters in length, and the spacing between the members 1 depends on the distance between the side columns, which, as previously discussed, is equivalent to accommodating three in The space used for vehicles in the parking level below the office floor, the distance can usually be anywhere from 6 to 9 meters. A side beam 16 extends between the side columns 2 , while a floor slab 4 extends between two adjacent elements 1 . The side beams 16 may comprise an internal steel beam which terminates short of the side of the side columns 2, so that it does not require any substantial connection to the columns 2, and is supported on the same outer surface of the supporting main structural member 1. On the support frame 19. The steel portions of the edge beams 16 are pre-arched to withstand static loads to minimize deflection along the edges of the building which could affect the glazing of any façade. It should be noted that in Figure 1, although only two beams are shown, any number of beams required to support a given floor area may be used.

Referring to Figures 3 and 4, the structure 1 basically consists of a shell, usually made of steel, comprising first and second (side shell) beams 5, which are in the shape of I-beams, having a web portion 30, At both ends of the web portion 30 there are first and second flange portions 31 and 32 . Extending from the lower part of the member 1 is a plate 13 (or forming a bracket-like soffit), usually made of metal, more specifically steel, whereby it rests on each bottom or side shell girder 5 The second flange portion 32 extends between, and is attached or otherwise engaged with the flange portion 32 . The shear stubs 12 extending from the web portions 30 of the side shell beams 5 are used to obtain integral action with the cementitious material poured into the interior space 57 of the shell formed by the beams 5 and plates 13 . A binding 23 of generally U-shaped form extends from within the floor 4 down into the interior space 57 and passes through the raised ribs of the panel 13 . This also serves as additional support for the cementitious material poured into the interior of the shell. Furthermore, reinforcement bars 24 are also provided in the component 1 . A closure or spacer 15 is also positioned within the floor 4 to tie the cage structure to the side shell beams 5 . There are several prestressed tendon members 10 in number, which will be introduced below with reference to FIG. 2 .

It should be noted that the pairs of beams 5 and the various reinforcements for the beams can be prefabricated off-site in a controlled production line environment with their reinforcements 24 and ties 23, prestressed tendon members 6, 8 and 10 are transported to the site together with supports 15 which hold the steel tendon members in position. Tendon member 6 is for dead-end anchoring of one of the tendons 10, while tendon member 8 is a pressed metal form comprising a free-end anchoring recess. Two steel side shell girders 5 connected to brackets 25 for handling and conveyance enable the entire assembly of an 18 m beam, typically about 4.5 tonnes, to be delivered to the site and with a simple lifting method, its ends In place on pre-set support frames, referenced 18 and 19, with a support frame 20 in the mid-span.

Referring to Figure 2, at the core wall 3 of a building, the member 1 may be received adjacent to a tenon and tenon 22 in the wall 3, while the individual bars 14 and 17 are screwed into hoops 21, which are the top and bottom The reinforcement connection has been pre-embedded in the jump form (jump form) core wall 3, so as to connect the steel bars 14 and 17 respectively. At the other end of the beam, all that is required for the connection to the outer column 2 is that the connecting bars 14 and 17 extend the required length through the surface of the column 2 . These bars 14 and 17, together with the beam ties 11 at the ends of the member 1, are the only bars of the member 1 that need to be fixed on site.

Each end of each beam can be stepped, although the web passing through member 1 may contain small (up to 150mm diameter) through-holes for fire sprinkler pipes, sewage pipes, etc. The bottom flange portion 32 of the shell beam 5 can accommodate any major utility piping network without hitting the ceiling height. This can be seen more clearly in Figure 2, where the step 7 is shown so that the space 9 between the step and the core wall 3 or column 2 provides a network for such common piping (if required) Space. The step also allows to accommodate the active or tensioned ends for one or more prestressing tendons 10 . The tendons 10 are post-tensioned in situ and may comprise any number as required to be located in the interior space between the steel side shell girders 5 . One prestressing tendon shown in Figure 2 extends in the bottom flange portion 32 between the steps 7 and a further prestressing tendon 10 is shown extending the full length of the beam with an overhang, in other words , prestressed in a concave manner, the purpose of this is to provide an upward force or component that counteracts the force of 50% to 100% of the total static load, for these beams usually about 50-60% is sufficient , the remaining static and transient load capacity is provided by the steel shell and cementitious materials of the prefabricated beams. Dead loads are considered to include the slab itself, the weight of the beams, and permanently superimposed loads such as ceiling surfaces and slab finishes. The two steel side shell girders 5 are usually pre-arched so that, once the temporary support is removed, all deflections due to dead loads are accommodated. In fact, the steel side shell girders 5, the prestressed tendons and the concrete core filling the inner space of the paired beams 5, interact together to bear the total load. However, the beams 5 and tendons substantially prevent the tendon member from carrying any significant share of the load, and before the beam has deflected horizontally, due to the prestressed tendons plus the pre-arched steel side shell beams 5 in between Capable of bearing the total static load, therefore, the concrete will never be allowed to creep.

In use, prior to construction of the steel side shell girder 5, shear stubs and prestress tendons 10 and most of the beam reinforcement are fabricated off-site, while the reinforcement 14, 17 and lashings connected to the ends Object 11 was produced on site. The element 1 is then placed on its temporary support just short of the tenon 22 in the core wall and just short of the column at the other end. The bars 14 and 17 are then placed in their respective hoops, together with the lashings 11 placed on site, after which the pouring of the slab is carried out so that cementitious material or concrete in general is poured into the slab structure, allowing filling in the steel side shell In the main volume of the interior space 57 inside the beam 5 . The two steel side shell girders 5 and the cementitious The combination of (concrete) materials first acts integrally.

Therefore, the two steel side shell girders 5 significantly increase the axial steel content of the composite beam, which acts as a compressive member under the action of the prestressed load, so that the axial creep due to shortening of the beam causes Any loss of prestress will be minimal. Such a hybrid beam structure may then also have no total deflection due to static loading, or it may be provided with a slight upward residual camber before transient loading. The remaining solid concrete beams as uncracked sections assist the other two components and their deflection increases due to live loads and any other transient loads.

Since the outer column initially does not support any floor 4 and element 1, the floor 4 and element 1 and column 2 can be poured on the same day. The columns 2 can be poured while at the same time the reinforcement of the floor 4 between the floor formwork and the composite element 1 is installed. As you can imagine, with a well-organized workforce, even for large slab areas, three days or Even less than slab circulation can be achieved step-by-step.

The concrete portion of member 1 is apportioned, with a simplified fire design in Australia, to a load condition of 1.1 times the dead load plus 0.4 times the live load, and similar figures in other countries. Therefore, no fire protection or complex fire engineering analysis is required if this actually provides a solution. The combined capacity of steel and prestressed concrete beams is more than sufficient to carry the working load, which is typically 1.25 times the dead load plus 1.5 times the live load in Australia and similar figures are used in other countries.

Most codes set the deflection limit at 1/500 of the span for the added deflection due to any creep component of the dead load plus the deflection due to the live load plus the weight of the partition. Therefore, for a span of 18 meters, the limit is 36 mm. For any building with large internal spans parallel to and adjacent to the building sides, the slab adjacent to the column on the building side (where the deflection is zero) and near the internal beams (for steel girder slabs The amount of deflection difference between the mid-span deflections of the internal beams of the system (approximately 2.5 meters) is obviously too large. A more stringent deflection standard than the code is necessary. The present invention achieves, with its hybrid steel and concrete beams, a maximum incremental deflection of about 20mm or less for a span of 18m.

Referring to Figures 5 and 6, another embodiment of the invention is shown in which the structural member 1 is made of a single unitary or combined structure. Specifically, instead of a pair of opposing beams connected by a plate as in the first embodiment, the present embodiment in the drawings has a generally U-row channel defined by a pair of side walls 33 and 34 And the bottom 35 connecting the respective side walls 33 and 34 is formed. Preferably, the structure is made of steel. The upper portions of the side walls 33 and 34 have flange portions 36 and 37, respectively, for supporting the floor 4 of the portion.

Referring to Figures 5(a), (b), (c) and (d), structural members may be made from a single piece of steel plate, for example, using the Four corners (not welded). Alternatively, as shown in Figure 5(b), given a two-plate structure, the structure can be welded at point 42 and the four knuckles 38 to 41 maintained. In Figure 5(c) an alternate configuration of the structural member is shown, retaining the knuckles 38 and 41 but welding at points 43 and 44 to provide a three-plate structure. Finally, in Figure 5(d), five sheets of steel can be used, with no knuckles, and four welds at points 45, 46, 47 and 48 as shown.

The invention can also be used for shorter spans with shallower side shell steel beams, with or without prestressed tendons, and with or without notches at the bottom of the beam ends to accommodate the main utility piping network.

In the case of prestressed tendons for such shallow beams that do not have a common pipe step (double stress anchor point), then after the tendons have been prestressed and grouted, the anchorage can be placed on top of the slab that can be poured afterwards Prestressing is applied to the concave and convex mortise holes inside.

Referring to Figure 7, the present invention is applicable to road tunnels using the "cut and cover" approach as described above. This involves lifting into position the structural elements, which are already reinforced and prefabricated in position, using cranes of relatively low load capacity. This is in contrast to the extremely heavy precast prestressed concrete beam 49 used in the prior art system, which is shown in FIG. 8 . Heavy precast prestressed beams 49 require the use of extremely large cranes to lift such members. Referring to Figure 8, the beam 49 has a relatively thin flange 50 and top plate 51 for this application. Usually a waterproof layer or membrane 52 for waterproofing is required over the full extent of the board, which in turn requires a board 53 to protect it from wear. With the present invention, a watertight monolithic casting can be used and all this is dispensed with. Referring back to FIG. 7 , this involves the use of fluid blocking devices, specifically, the fitting of a water-stop sheet 58 and a partial waterproof layer 54 (or a waterproof film) to ensure the watertightness of the tunnel roof. The span of the floor slab between the structural elements 1 can be sufficiently thick and poured in sections with suitable dimensions, prestressed if necessary between the control joints 56 . A waterstop 53 and a partial waterproof layer or membrane 54 are fitted to each control joint 56 .

Referring to Figure 9, as noted above, the present invention is also applicable to large multi-span floor spaces, particularly high floor-to-floor dimensions, and/or large spans in one or two directions, and/or such as for retail High floor loads on floors for commercial, recreational or other uses. The building elements 1 may be used to span between the columns 59 to which the secondary beams 60 are bolted to support the floor slab 4 between the structural elements 1 .

Simply supported between columns during construction, the structural member can be fabricated to span the self-weight of the floor structure plus the live load during construction.

The structural members then form a reinforced concrete or prestressed concrete member which is continuous over multiple spans for the loads to be supported by the floor slab.

Claims (40)

1. A structural member of a building comprising: a pair of beams, each beam in the pair having a first flange portion, a second flange portion, and extending between the first flange portion and the second flange portion a web portion; a plate adapted to engage with one of said first flange portion or said second flange portion of each beam such that a an internal space; Wherein, the cementitious material occupies the main volume of the internal space to form a non-integral building structural member, and after applying post-tensioning prestress, under static load, the structural member of the building has Residual deflection or no deflection. 2. The member of claim 1, further comprising one or more steel bars extending along the length of the interior space. 3. A member as claimed in claim 2, wherein said one or more reinforcing bars are each prestressed to provide an upwardly directed force which counteracts a portion of said dead load. 4. The element of claim 1 for supporting a long-span floor area in a building. 5. The member of claim 4, wherein the first flange portion of each beam supports a portion of a floor span in the building. 6. A member as claimed in claim 5, wherein one end of the member is fixed to a column of the building and the other end of the member is fixed to the core of the building. 7. A structure as claimed in claim 6, wherein said structure is temporarily supported on scaffolding at said ends of said structure prior to securing said ends of said structure. 8. The member of claim 1, wherein the member has one or more shear studs extending from said web portion in each said beam into said interior space to communicate with said The cementitious material forms a whole. 9. The structure of claim 1 wherein support means in the form of a lashing extends into said interior space to support said cementitious material. 10. The member of claim 1, further comprising a plurality of steel bars extending along a portion of the member. 11. A member as claimed in claim 10, wherein said other end of said member is received within a tenon and tenon abutting within said core of said building. 12. A member as claimed in claim 11, wherein individual hoop means formed in said core are secured to individual bars of said plurality of bars. 13. The member of claim 1 wherein each end of each beam is stepped to accommodate a common conduit. 14. The structure of claim 1 wherein each beam in said pair of beams is constructed of metal. 15. The member of claim 1, wherein the cementitious material is concrete. 16. A building structural member comprising: a generally U-shaped trough means having a pair of opposing side walls and a further portion connecting the side walls; wherein said pair of opposite side walls and said other portion form an interior space; and wherein the cementitious material occupies the main volume of the interior space to form a non-integral building structural member in the trough device, and the building is under static load after post-tensioning prestressing The structural members of the object have residual deflection or no deflection. 17. A member as claimed in claim 16, wherein the member has one or more shear stubs extending from each of said side walls into said interior space to be integral with said cementitious material . 18. A structure as claimed in claim 16 wherein support means in the form of a lashing extends into the interior space to support the cementitious material. 19. The member of claim 16, further comprising one or more steel bars extending along the length of the interior space. 20. A member as claimed in claim 19, wherein said one or more steel bars are each prestressed to provide an upwardly directed force which counteracts a portion of said dead load. 21. The structure of claim 16 wherein each of said side walls has a flange portion extending from a free end of each side wall, said flange portion supporting a portion of the floor. 22. The member of claim 16, wherein each end of the member is secured to a support structure. 23. A member as claimed in claim 22, wherein the member is temporarily supported on scaffolding at each end of the member prior to securing each end of the member to the support structure . 24. The member of claim 16, further comprising a plurality of reinforcing bars extending along a portion of the member. 25. A member as claimed in claim 24, wherein at least one of the two ends of the member is received within a rebate abutting within the support structure. 26. A member as claimed in claim 25, wherein individual hoop means formed within the support structure are secured to individual bars of the plurality of bars. 27. The member of claim 16 wherein each end of each beam is stepped to accommodate a common conduit. 28. The member of claim 16, wherein the groove is unitary in construction. 29. A component as claimed in claim 16, wherein the channel means is formed by one or more joints connecting adjacent parts. 30. The component of claim 16, wherein the channel means is constructed of metal. 31. The structure of claim 16, wherein the cementitious material is concrete. 32. A structure as claimed in claim 16, wherein the floor has fluid blocking means to ensure that the structure is fluid tight. 33. A member as claimed in claim 32, wherein said fluid blocking means comprises a fluid blocking member and a fluid resistant membrane. 34. A building structural member comprising: a pair of beams, each beam in the pair having a top flange portion, a bottom flange portion, and a web portion extending between the top flange portion and the bottom flange portion ; a plate adapted to engage a corresponding bottom flange portion of each of said pair of beams such that an interior space is formed within each of said pair of beams and said plate; as well as Wherein, the cementitious material occupies the main volume of the internal space to form a non-integral building structural member, and after applying post-tensioning prestress, under static load, the structural member of the building has Residual deflection or no deflection. 35. The structural member of claim 34, wherein said panel is a soffit. 36. A structural member as claimed in claim 35 wherein said soffit is a soffit in the form of a metal bracket. 37. A method of making a structural member of a building, comprising the steps of: constructing a pair of beams, each beam in the pair comprising a first flange portion, a second flange portion, and extending between the first flange portion and the second flange portion a web portion of; forming and assembling a panel so that the panel engages one of said first flange portion or said second flange portion of each beam such that a pair of beams and said panel form a interior space; and pouring cementitious material into said interior space to form a non-integral building structural member such that, after said cementitious material has hardened and post-tensioned prestressed, said building The structural members of the object are basically deflection-free. 38. The method of claim 37, wherein the pouring step includes pouring the cementitious material as part of a slab into the interior space in the same step as an adjacent slab. 39. The method of claim 37, wherein said pouring step includes pouring said cementitious material to construct a floor, and said pouring is performed separately from the pouring step in constructing said floor. 40. A method as claimed in any one of claims 37 to 39, further comprising initially supporting the end of the structural member on a temporary support structure adjacent to the permanent end support of the structural member .

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