Badar (BAZ)

It is 25% of base shear. Yes, something like that.

Yes there is; read the section 1630.9.2 of the UBC 97.

What do you mean by modifying SMRF in ETABS. What do you want to modify about special moment resisting frame. The moment capacity of columns at the joint for most unfavorable loading conditions should be equal to or more than 20% the moment capacity of beams framing into the joint.

If shear demand of structural wall is more than the capacity due to seismic forces, and if the frame can take fifty percent of base shear, satisfying the drift requirement for that 50% share, then can this lead to the collapse of structure.

Can shear failure of structural walls trigger collapse of reinforced concrete building if the building satisfies drift limits and its frame can independently take 50 percent of seismic force in both directions.

Read the section 14.4 of ACI 318-11 for axial capacity of the RCC wall. There should be some option of displaying axial forces in shell members in SAP.

I have observed few issues while getting the design results of reinforced concrete members from ETABS (v 9.7.4). I wanted to share this issues with you and get your input and observation on it. ETABS always considers the minimum eccentricity for selecting the design moment of columns irrespective of the probable behavior of the column, whether short or long column. See section 10.10.6.5 and its commentary of ACI 318-08 which deals with minimum eccentricity of long columns. You should always check the design moments that ETABS uses for columns if you want to bring down the cost of construction. If your model has lateral loads, ETABS will give you design moments in column irrespective of its status as braced or un-braced as per ACI 318 criteria. You should investigate if the storey under consideration is braced, or un-braced (10.10.5.2), and decide appropriate design moments of columns. ETABS has a tendency to select a time period of the building that is considerably less than the value obtained by the approximate method, Method A, of the section 1630.2.2 of UBC 97. To quote the FEMA 451 document: ''Because this formula is based on lower bound regression analysis of measured building response in California, it will generally result in periods that are lower (hence, more conservative for use in predicting base shear) than those computed from a more rigorous mathematical model". So, there is no need to use the value of time period that is lot less than Ta. One should always check the time period used by the software; ETABS can overestimate the seismic force by more than 2 times. Method A gives lower T and higher V, so FEMA 451 has advised not to use the value of time period less than this value even if rigorous analysis gives a lower value. I have seen the results where Etabs have use the value of time period less than Ta; in-fact as low as 0.5Ta, which can increase the base shear two times.

Even though the structure is not indented to be supported as mentioned in topic of the thread, Truss can be supported as cantilever by exhibiting classical truss action (tension and compression members). Answering your question Tension in top chord, compression in bottom and moment arm between them at any cross-section will resist bending moment at that section. Shear at any cross-section will be resisted by tension and compression in web members. The moment at the support will be resisted by the reaction-couple at the support.

The statement shows your observation.What is your question?

The compensation will be in line with what other engineers of similar experience are getting in the market. There will not be any probation.

Arif Consulting Engineers is looking for a person who is interested in practicing structural engineering with them. Interested candidate should have some earlier experience in the field, preferably 4-5 years. Contact details of the company can be found out at http://www.aceconsults.com/

1: You can increase the bearing capacity by 33%.But this recommendation is reasonable for dense granular soils, stiff to very stiff clays or hard bedrocks; it is not applicable for loose soils susceptible to liquefaction, or increase in pore water pressure. 3: Yes, it is normal to get uplift. We use service combos for checking bearing pressure and strength design combos for the reinforcement in the raft. 4: If you have provided minimum reinforcement, and satisfied maximum spacing requirements of the code, you don't need to check crack widths. If more than 80 percent of your raft area satisfy the limit of bearing capacity then settlement wont be a problem. 5: One can neglect that localized increase in bearing pressure.

Assign them one name; it is not possible to have two diaphragms at one level. One structural system can only have one diaphragm at any level. Two diaphragms means two independent structural systems.

Increasing the depth of beam will also reduce the drift.

Engr Uzair gave the appropriate reply to the query

For that, you need to read chapter 14 of ACI 318-11, or earlier version.

Yes, we do consider it.

Rest is assumed to have lost to cracking.

It is not convenient and practical to have ties spaced at less than 4 inches. I would say that increase the area of hoops and increase the spacing of hoops.

if the structural system of office space is connected to shear-wall structural system of bunker, then gravity loads will control the design of the structure of office space. You can consult chapter 10 of ACI 318-11 to know if frames of office space are sway, or non-sway.

For short column, the code does not require us to consider minimum eccentricity. The accidental eccentricity has already been taken into the account in equations of design strength.

It shouldbe OK if you have atleast provided temperature and shrinkage reinforcement

In author's defence, it is not normal to look for errors in concept that everybody has accepted. Critical analysis of one's own work, when no one is challenging it, is highly appreciatable.

The document starts with the statement, "Ray Clough and I regret we created the approximate response spectrum method for seismic analysis of structures in 1962". Termination.pdf

Yes. Why it would'nt be?