JackEngTip
Structural
- Feb 19, 2019
- 14
Hi, I am seeking some help from you guys for a 5-storey building (with no basement) that I am designing. The slabs are concrete and are supported by steel beam-column frames and a concrete core wall that located on the north-east corner. The soil condition from the soil report: 0-3m: FILL, 3-7m: stiff clay (with 300kPa allowable capacity and 25kPa skin friction). My questions are as follows:
1. I am going to use piers for the core walls. Normally if I use Mat foundation I will treat it as eccentrically loaded pad(work out the axial compression of core under G+Q together with the overturning moment from wind & earthquake and the see if the bearing capacity is okay). While for piers supporting core walls, should I envelope the axial compression under wind and earthquake to check the bearing capacity of soil or do I use G+Q only? And if the answer is the later one then why?
2. There are high rise buildings (30+ storey) on both sides. In this case, can I still use skin friction to increase the soil bearing capacity? Is it really safe to do so? What about the negative skin friction caused by the adjacent high rise buildings?
3. Even if the capacity is fine, what about the deflection? Is it okay for multi-storey structure footings like this to be founded on silty clay instead of rock? How do I work out the vertical deflection of the piers without complex analysis?
4. Should the steel beam-column frames to be portal frame so they can resist lateral loads like wind and earthquake? I have seen too many engineers use the core wall only to resist lateral loads but I doubt that as the core is eccentrically located, torsion will be introduced under earthquake. What's your thoughts on this?
Thank you in advanced.
1. I am going to use piers for the core walls. Normally if I use Mat foundation I will treat it as eccentrically loaded pad(work out the axial compression of core under G+Q together with the overturning moment from wind & earthquake and the see if the bearing capacity is okay). While for piers supporting core walls, should I envelope the axial compression under wind and earthquake to check the bearing capacity of soil or do I use G+Q only? And if the answer is the later one then why?
2. There are high rise buildings (30+ storey) on both sides. In this case, can I still use skin friction to increase the soil bearing capacity? Is it really safe to do so? What about the negative skin friction caused by the adjacent high rise buildings?
3. Even if the capacity is fine, what about the deflection? Is it okay for multi-storey structure footings like this to be founded on silty clay instead of rock? How do I work out the vertical deflection of the piers without complex analysis?
4. Should the steel beam-column frames to be portal frame so they can resist lateral loads like wind and earthquake? I have seen too many engineers use the core wall only to resist lateral loads but I doubt that as the core is eccentrically located, torsion will be introduced under earthquake. What's your thoughts on this?
Thank you in advanced.
