Wall Girts

Load calculations braced frames 12-39—12-43 columns 11-37—11-40 exterior walls 11 4—11-10 foundations 11-41—11 45, 12-43—12-46 rigid frames 12-31 — 1 2-39 roof beams 1 1-27—1 1-31 roof decking 12-6—12-71 roof girders 1 1-36 roof putins 1 2-16—1 2-26 roof slabs, in-plane 1 1-1 1 — 1 1-16 roof slabs, out-ofplane 1 1-21—1 1-26 side walls, in-plane 11-16—11-20 wall girts 12-26—12-30 wall panels 12-12-12-16... 

A typical shear connection for a wall girt might consist of a relatively thin two bolt shear tab. As a blast load is applied to the girt, tearout of the tab may occur due to an inadequate number of bolts or insufficient weld capacity. This will prevent development of plastic moment capacity of the member and thus reduce its blast resistance. A typical upgrade for this type of connection is addition of a new shear tab wetded or bolted to the existing column and girt. 

Many roof beams, roof purlins and wall girts in existing petrochemical structures are not capable of developing their full plastic moment capacity for loads in the plane... 

Two methods for applying blast loads will be used. The first is the Tributary Area Method which applies the wall panel pressure-time history to the loaded area of the girt. The second method will use the dynamic reactions of the wall panel as the load applied to the girt. The girt load is determined at each time step as follows ... 

Load, psi (2 sides) (wall pane reaction, Ib/in] / (36 in girt spacing)... 

The braced frame must develop the ultimate capacity of the members which it supports, namely the girts and end wall columns. The force applied to the top of the column is equal to the tributary area times the resistance as a static load. Each braced frame will be designed to resist the entire load even though there will be a frame at each end of the building. This will provide redundancy and will eliminate large axial forces in the top perimeter beams at the interior frames. 

Option 3 Add a new girt/steel cladding system exterior to the existing wall. 

FIGURE 10.8 Wall Upgrade With Girt/Stcel Cladding System... 

Metal panels and girts along the long sides will load the main frames of the building, Loads on the back wall will be ignored to maximize Sidesway. Reactions form these members will be transferred to the frame. Loads on the side walls will be resisted by braced frames in the end bays. 

Note that the wall panel has a period, tn, of 7.2 ms. Analyzing the wall panel and girt separately should be adequate with this difference in periods (refer to section 6.2.3). 

FURTHER DAMAGE TO WALL PANELS DAMAGE TO GIRTS... 

Girt (in systems-engineered metal buildings) means a Z or C shaped member formed from sheet steel spanning between primary framing and supporting wall material. 

In the evaluation of blast damage to structures, a distinction should be made between local and global response of structures. Local response would be associated with response of wall elements relative to their supporting members (girt, purlin, beam and column). For local structural elements the blast and dynamic wind loads are typically associated with only their load on the local structure. 

---