seismic/wind design 7

[haynewp]

If you have a building whose overall lateral design is controlled based on wind force, however the seismic loads are pretty substantial as well, shouldn't the anchorage checks for concrete be investigated for seismic anyway? The UBC gives several equations for these anchorage checks. I have seen a lot of engineers decide that wind controls a building design and design all connections based on this. I think you could have larger seismic pull out forces (due to the back and forth motion) for example at connection of diaphragm to tilt walls. Does anyone else agree?

 

[ishvaaag]

If you have to check some seismic loadcases, the anchor of its (seismic) forces no doubt need be checked acording to the seismic provision applicable. If done this wind controls anywhere and any detail then it would be how the others say, but in other case, no. Furthermore, for some hypothesis that need to take unto account the real layout of reinforcement, the biggest and real reinforcement from wind or EQ should be input for the anlysis or check.

 

[JAE]

haynewp,

One of the most ignored issues in structural design is in areas where wind loads tend to "control" the design over seismic.

The correct procedure is to develop the loads for both wind and seismic and then design your structural elements for the controlling factor. Too often, engineers determine that the wind is just a little larger, overall, than the seismic, and then proceed to design the entire structure for wind only, ignoring the seismic issues that still actually apply.

For example, while an overall wind load may control the design of a lateral deck diaphragm and brace design, the code requires, in the case of the sligtly lower seismic loads, to factor up the seismic in connection design to ensure that the member fails before the brace. Thus, a steel chevron brace may be based on a controlling seismic load, and its connections as well, while the floor or roof diaphragm may actually be controlled by wind.

It is incorrect to just discard seismic just because the overall primary seismic force applied to the structure is less than the wind load. Both wind and seismic loads must be carried through the entire design, all the way to the foundation, checking each to see which controls in each "piece" of the structure.

 

[StructuralDzine]

JAE,

A good reply.

Regards