Expert: Arshad Khan - 8/18/2010

Question
QUESTION: Dear Sir,

I have few questions regarding ETABS, hope you can help me clear these points:

1.In the Global Force Balance the OTHER load cases show
 values close to zero.   However, the Temp case shows +
 98.8 or values greatly above zero,
      a) why the value is not close to zero (0) ?
      b) what does this mean?.

2. For the Options/ preferences/ shear wall design, the    
  default value for IP max is 0.02,  
     a) what is the basis of this limit? and
     b) what is the maximum ratio we can use as per code?

Thanks and my warmest regards,

socket


ANSWER: Hi Socket,

1. The reason you have a net support reaction is that temperature loading is an internal load, and unless your supports are free to accommodate the strain caused by temperature rise/decline, you will have some net support reactions.

2. The explanation about what values to use for IP-max and IP-min are in the technical manuals that you can access from the Computers & Structures>ETABS9>Manuals on your hard-drive. An extract is attached for your info

---------- FOLLOW-UP ----------

QUESTION: Dear Sir,

I appreciate much your clear and prompt reply.
However, I have a follow up question for my 2nd item.

The pier i designed fails in flexure as it requires a r.ratio of 0.029 for this reason i set IPmax to 0.03,
but it is not clear to me the following:
a) the implication of setting the IPmax outside its default
  value
b) the code provision for max. r. ratio for piers?

 Hope you can help me clear these issues.


Thanks and my Warmest regards,

Socket

p.s.
due to architectural reqt's the pier size cannot be modified

Answer
Hi Socket,

That depends on which code you use, but in any case you should proceed with the design and check that the rebar percentages and concrete/rebar stresses are within allowable limits.

Alos read the Shear Wall Design UBC technical manual, E-TN-SWD-UBC97-006, pages 17 & 18, for an explanation of IPmax/min.