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FW: Concrete Movement Joints[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "'seaint'" <seaint(--nospam--at)seaint.org>
- Subject: FW: Concrete Movement Joints
- From: "La Count, Curt" <Curt.LaCount(--nospam--at)Jacobs.com>
- Date: Thu, 2 Sep 1999 13:02:00 -0700
The size of the joint depends on the movement of each building. 100mm would obviously not be suited for a 20 story building (especially given construction tolerances for out of plumb). My comments concerning 100mm joints were based on experience and a 1 story building. By the 1994 UBC (to make it easier to discuss), drift is limited to .005h. For a 4m story the allowable drift is 20mm. This value needs to be amplified for inelastic displacements based on the structural system but in general the value is a factor of 3. Since each building could move this value towards each other the joint should be 2 x 3 20mm, which is 120mm, so I rounded down for simplification. The most common joint width I've worked with, based on mid rise buildings is 150mm. A 25mm joint would have to be for an extremely stiff building or as I suspect is common, building seismic movements are not considered or deemed improbable. Curt La Count Jacobs Engineering Portland, OR ---------- From: Hasan Hindawi To: seaint(--nospam--at)seaint.org Subject: Re: Concrete Movement Joints Date: Thursday, September 02, 1999 12:52PM As you mentioned certain measures could be taken to reduce slab cracking due to drying shrinkage. However, in my opinion , these measures do not help in reducing flexural stresses in edge columns/shear walls resulting from temperature changes.Those flexural stresses could be quite high depending on building length, edge column stiffnesses, ... ,etc. My question engineers in seismic areas, does a 100mm wide expansion joint suffice to prevent pounding, taking into consideration the allowable drift for high-rise buildings. Hasan Hindawi ----- Original Message ----- From: La Count, Curt <Curt.LaCount(--nospam--at)Jacobs.com> To: 'seaint' <seaint(--nospam--at)seaint.org> Sent: Thursday, 02 September, 1999 5:57 PM Subject: Concrete Movement Joints > On our projects, we've been more concerned about drying shrinkage than > temperature movements. Typical drying shrinkage movements are .06 %, while > temperature movements are typically .1% per 100 degrees C. It takes about > 60 degrees C to equal drying shrinkage. Control of the design mix, > distributed steel reinforcing, fiber reinforcing and pour sequencing are > methods we've used to pour plates as large as 80m, with only minor cracking. > > > I have found it common practice, in non-seismic regions, to provide > expansion joints in buildings with very small joints. The effects of > pounding were apparently never investigated or the probability of occurrence > thought to be remote enough to ignore. On the West coast of the US, > engineers would typically think 100mm joints as minimum separations to > prevent pounding. > > Curt La Count > Jacobs Engineering > Portland, OR > > > ---------- > From: Rex Donahey > To: seaint(--nospam--at)seaint.org > Subject: RE: SEISMIC DESIGN to UBC'97 > Date: Thursday, September 02, 1999 6:28AM > > A major factor in cracking of large structures is shrinkage of the concrete > during the construction phase. Although it can require a great deal of > coordination, it is possible to detail closure strips in the building. If > the strips are left open for at least 30 days, they will allow most of the > shrinkage to occur with less constraint.
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