Lateral displacement vs thermal expansion

[jedge]

I'm reponsible for designing an enclosed and air conditioned bridge connecting two academic buildings at a 45 degree angle to each facade. The walls of the bridge are all glass. The structure is composed of two vierendeel trusses spanning 61 feet between freestanding 32-foot tall concrete encased wide-flange columns. Architectural constraints prevent the columns from being designed stiff enough to adequately limit lateral displacement of the bridge due to wind load and unbalanced live load. I wish to use the buildings to limit this displacement resulting in a maximum load to the building of 10 kips. If the connection prevents movement due to thermal changes, a 40 deg F temperature change increases the load to 450 kips and the steel members become overstressed. I wish to utilize a teflon bearing pad or a pot bearing to permit 1/2" lateral movement. After that movement is taken up, I want the connection to transmit the 10 kips to the building concrete floor framing thereby limiting the maximum lateral displacement to 1/2". Is this reasonable? I'm not familiar with teflon bearing pads or pot bearings. How would the range of movment be restricted? Please help.

 

[JedClampett]

I would fix one side laterally and axially. On the other side I would install a sliding pad like you described. Within this pad install metal pins in the support and slotted holes in the bridge. These pins can take forces perpendicular to the span. This won't allow a variable load like you want, but it might solve your problem.

 

[dlew]

jedge,

I understand the force transmitted to the building can not exceed 10 kips. Is that right?

If so, you could also consider the use of spring loaded pads, similar to those used as shock absorbers for vibrating equipment, connected on the sides of the bridge to limit the horizontal force transmitted to the buildings while allowing the bridge to deflect laterally.

To let the bridge move 1/2" and then hit the existing buildings does not seem to be a good idea, unless there is a resilient material between them to absorb the impact.

The teflon bearing pads under the bridge would take the thermal longitudinal elongation.

Regards

AEF