Expansion Joints and Horizontal Drift.
Expansion Joints and Horizontal Drift.
(OP)
Greetings to everyone,
I am having a bit of a dilemma, I have a structure that is L shaped.. the long dimension is 200 feet and the short is 115 feet. Its steel deck and steel moment frames, with the assumption of pinned bases. I am trying to ascertain the necessity of an expansion joint due to thermal effects, temperature here is around 104F on very hot days and 68F on very cool days. I have read the Federal Construction Council Federal Report No. 65, and it seems to me that this particular structure could be built without expansion joints. However it is common practice here to add expansion joints when the structure is long, the common method is to use a double line of columns. My doubt arises from the fact that this is a seismic area, after modeling the structure as two separate buildings I am getting drifts on the top floor of around 4cm; it would seem to me that then the expansion joint would have to be 8 or 10cm wide in order to accommodate movement of the structures during an earthquake. Is this correct? an 8cm expansion joint seems very wide.
Thanks.
I am having a bit of a dilemma, I have a structure that is L shaped.. the long dimension is 200 feet and the short is 115 feet. Its steel deck and steel moment frames, with the assumption of pinned bases. I am trying to ascertain the necessity of an expansion joint due to thermal effects, temperature here is around 104F on very hot days and 68F on very cool days. I have read the Federal Construction Council Federal Report No. 65, and it seems to me that this particular structure could be built without expansion joints. However it is common practice here to add expansion joints when the structure is long, the common method is to use a double line of columns. My doubt arises from the fact that this is a seismic area, after modeling the structure as two separate buildings I am getting drifts on the top floor of around 4cm; it would seem to me that then the expansion joint would have to be 8 or 10cm wide in order to accommodate movement of the structures during an earthquake. Is this correct? an 8cm expansion joint seems very wide.
Thanks.






RE: Expansion Joints and Horizontal Drift.
The later US code (IBC / ASCE 7) now allows use of a square root of the sum of squares of the two buildings when determining joint width I believe.
RE: Expansion Joints and Horizontal Drift.
RE: Expansion Joints and Horizontal Drift.
I had that condition only once with a site that had a fault through it and we switched foundation types across it.
RE: Expansion Joints and Horizontal Drift.
RE: Expansion Joints and Horizontal Drift.
I don not know what code or method is being used for the analysis. With ASCE 7, the elastic drift needs to be multiplied by a deflection amplification factor when sizing building separations. A building is expected to undergo inelastic deformation during the design earthquake. The deflection amplification factor is a simple way to account for this.
The architect needs to know the separation dimensions early in the design process. Also, the drift needs to be coordinated with the cladding. For instance, many curtain walls can take sizeable in plane deflections (drift). But the maximum drifts allowed by the code may require special connection detailing between the cladding and the structure. Often times, it is better to stiffen the building to reduce the drift, than deal with all of the consequences with cladding and other architectural elements.