GB2128217A - Portal frame buildings - Google Patents

Abstract

A portal frame building has a number of portal frames whose legs 2 are rigidly fixed to foundation blocks 8. The legs 2 are offset with respect to the centres of the foundation blocks towards the middle of the frames, whereby a torque is developed, tending to turn the upper ends of the legs inwards. <IMAGE>

Description

SPECIFICATION Portal frame buildings The present invention relates to portal frame buildings. As is well known, such buildings, which are widely usedforwarehousing and light industrial purposes, commonly comprise a number of portal frames spaced along the length ofthe building and defining bays of the structure. Each of the frames usually consists oftwo vertical legs and a pair of roof beams which slope upwards from the tops ofthe legs to the ridge of the roof and span the width of the building. The frames are commonlyfabricated in steel, though in smaller structures reinforced concrete is used.

Each frame, or in some cases each of two halfframes joined together at the roof ridge, is of unitary construction, that is to say its part are rigidly connected togetherto form a continuous member which maintains the required shape without bracing by virtue of its own stiffness and resistance to bending.

Whilethisisthecommonestform of portal frame building others may have legs which are inclined out of vertical and roof beams which at least in part are horizontal or slope downwards. Multiple frames can also be used which have three or more legs with roof beams extending between each pair of legs.

The feet of the frames rest on foundations which are designed to carry the vertical loads resulting from the weight of the portal frames and ofthe roofing and walling which are carried by the frames. Allowance also has to be made for horizontal forces resulting from imposed loads such as wind forces and materials resting againstthe sides ofthe building and also from bending of the frames under vertical loads, for examplethose resulting from snow on the roof or machinery suspended from the two frames. In designing the steelworkfortheframes one of two assumptions is commonly made regarding the support of the frames bythefoundation.The first assumption is that thefoundation is sufficiently massive and the connection between the frame and the foundation is sufficiently rigid forthefeetofthe legs to be held rigidly in position. While this first assumption reduces the demands on the steelwork it generally results in a greater total expense for frames and foundations than the second assumption, which is that the foot of each leg is free to hinge with respect to the foundation. In practice this may be true even if the steelwork is bolted to the foundation either because the connection is insufficiently rigid to prevent movement of the leg or because the subsoil is sufficiently elastic to permit movement of the leg. Underthe second assumption lighter and cheaperfoundations can be used.

It is not uncommon forthe steelwork and the foundations to be separately designed,the loads to be sustained bythefoundations being specified by the designer of the steelwork, the latter having to take into account the degree of bending and distortion ofthe portal frames which is acceptable under expected loadings. Thus although foundation designers have from time to time made improvements in the methods of designing foundationsto suitthe loadsspecified by the steelwork designers and to meet special site requirements, little attention has been paid to the interaction of the frame and the foundation.

In accordance with the present invention there is provided a portal frame building wherein means are provided at or near the foot of a number of portalframe legs to withstand outwardly directed forces while downwardly directed forces are separately supported by foundation blocks, each of the said legs being rigidly fixed to a foundation block in such a way asto preventthe leg pivoting with respecttothe foundation block, and in which each of the said legs is offset with respect two the centre of the foundation blocktoward the middle of the frame whereby a torque is developedtending toturnthe upper end of the leg inwards.

With such a construction it is possible to design the foundations in conjunction with the steelwork in order to give optimum resistance to loading at reduced total cost. In particular it will commonly be possible to reduce the cost of the steelwork relative to that designed on the basis of the second assumption, namely hinging ofthe legs, while using the same foundation to carry the vertical load.

The means forwithstanding horizontal loads may take the form of a tie extending between the feet of the legs of each frame but more conveniently may consist of an anchor four each leg which is embedded in the floor of the building. Alternatively an abutment may be provided on the outside of each leg but this should be separate from the foundation block to avoid interfering with the development of the required torque on the leg.

The invention will be described in more detail with the aid of an example illustrated in the accompanying drawings, in which: Fig lisa section of typical portal frame building in accordance with the invention, Fig 2 is a detail, on an enlarged scale, ofthe part of one leg of a portal frame and its foundations, and Fig 3 is a plan view on the line Ill-Ill of Fig 2.

A portal frame 1 comprises two vertical legs 2 and a pair of roof beams 4. As is best shown in Figure 3, the legs 2 are of I-section, and a fixing plate 6 is welded to the lower end of each leg. Each leg 2 is rigidly fixed to a concrete foundation block 8 by means of bolts 10 passed through the fixing plates 6 and into the foundation blocks. Each leg 2 is offsetwith respect to the centre of its foundation block 8 by a distance A towards the middle of the frame, as indicated in Figure 2.

Each leg 2 is provided near its base with a hole 12 through its central plate 14. Av-shaped anchor 16 passes th rough each hold 12, the arms 18 of each anchorthen projecting inwardly and being embedded in the floor 20 of the building. By means ofthese anchors the portal-frame legs can withstand horizontal outwardly-directed forces.

Itwill be appreciated thatthere may be occasions on which it is required to offsetthe legs of the portal frame with respect to their foundation blocks towards the outside oftheframe. Such an offset may be required, for example, for the shorter legs of a portal frame building built on a slope.

CLAIMS (Filed on 15/10/83) 1. Aportal frame building wherein means are provided at or near the foot of a number of portalframe legs to withstand outwardly directed forces while downwardly directed forces are separately supported by foundation blocks, each of the said legs being rigidlyfixed to a foundation block in such a way asto preventthe leg pivoting with respectto the foundation block, and in which each of the said legs is offset with respect to the centre of the foundation blocktoward the middle ofthe frame whereby a torque is developed tending to turn the upper end of the leg inwards.

2. A building according to claim 1 wherein the means for withstanding outwardly directed forces comprises a tie extending between the feet of the legs of each portal frame.

3. Abuilding according to claim 1 whereinthe means forwithstanding outwardly directed forces comprises an anchorfor each leg embedded in the floor of the building.

4. A building according to claim 1 wherein the means for withstanding outwardly directed forces comprises an abutment provided on the outside of the leg but separate from the foundation block.

5. A building substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. which it is required to offsetthe legs of the portal frame with respect to their foundation blocks towards the outside oftheframe. Such an offset may be required, for example, for the shorter legs of a portal frame building built on a slope. CLAIMS (Filed on 15/10/83)

1. Aportal frame building wherein means are provided at or near the foot of a number of portalframe legs to withstand outwardly directed forces while downwardly directed forces are separately supported by foundation blocks, each of the said legs being rigidlyfixed to a foundation block in such a way asto preventthe leg pivoting with respectto the foundation block, and in which each of the said legs is offset with respect to the centre of the foundation blocktoward the middle ofthe frame whereby a torque is developed tending to turn the upper end of the leg inwards.

2. A building according to claim 1 wherein the means for withstanding outwardly directed forces comprises a tie extending between the feet of the legs of each portal frame.

3. Abuilding according to claim 1 whereinthe means forwithstanding outwardly directed forces comprises an anchorfor each leg embedded in the floor of the building.

4. A building according to claim 1 wherein the means for withstanding outwardly directed forces comprises an abutment provided on the outside of the leg but separate from the foundation block.

5. A building substantially as hereinbefore described with reference to the accompanying drawings.