Allowable vertical deflection of footbridge
Allowable vertical deflection of footbridge
(OP)
Hello all.
I'm looking at the design of a footbridge. The form of the bridge is a steel through girder vierendeel truss.
I have been looking in BS 5400 for an indication of deflection limits under dead + imposed loads. There do not appear to be any such limits in BS 5400, but there is a statement that the deflection should not affect the servicability of the bridge, or affect the applied corrosion protection.
I wondered what type of limits other engineers employ on such structures? The deck is to be stiffened steel plate, and as such there are no brittle finishes.
VB
I'm looking at the design of a footbridge. The form of the bridge is a steel through girder vierendeel truss.
I have been looking in BS 5400 for an indication of deflection limits under dead + imposed loads. There do not appear to be any such limits in BS 5400, but there is a statement that the deflection should not affect the servicability of the bridge, or affect the applied corrosion protection.
I wondered what type of limits other engineers employ on such structures? The deck is to be stiffened steel plate, and as such there are no brittle finishes.
VB






RE: Allowable vertical deflection of footbridge
RE: Allowable vertical deflection of footbridge
RE: Allowable vertical deflection of footbridge
Here in New England, the major supplier of pedestrian bridges limits vertical deflection of the main trusses due to pedestrian live load to 1/400 of the span, unless specified otherwise. Other members such as floorbeams and stringers are limited to 1/360 of the span.
RE: Allowable vertical deflection of footbridge
Dependent upon who will be using this bridge, general public or manufacter/construction workers, "structural aesthetics" will play an important role. For instance, if a 3/8" sag rod could support the whole bridge, place a 2" diameter pipe around the 3/8" sag rod.
Also keep an eye on vibration, a little extra dead load may be beneficial to dampen out foot traffice on a light structure.
RE: Allowable vertical deflection of footbridge
RE: Allowable vertical deflection of footbridge
I'll limit deflection to L/500 under live loads.
I also take on board the comments regarding vibration. Here in the UK the Design Manual for Roads and Bridges specifies a minimum natural frequency of 5 Hz for vibration in the vertical plane, and 1.5 Hz in the horizontal plane.
Thanks again !!
VB
RE: Allowable vertical deflection of footbridge
RE: Allowable vertical deflection of footbridge