SEFP Topics Feedhttp://www.sepakistan.com/rss/1-sefp-topics-feed.xml/Get the latest and greatest updates on topics under discussion.enModelling Issues/consideration in ETABSI want to comment on some modelling issues in ETABS. Though some of these things are discussed elsewhere in the forum, I hope to extract some more useful conclusions.
First thing is related to modelling the bending stiffness of flexural members, for strength level loads, that is representative of their condition near failure.
The ACI code specifies the modifier of 0.35 on gross moment of inertia to represent its condition at yielding.
Some people say that the factor should be multiplied by 2 to represent the stiffness of T-beam. This approach would be justified if you are not taking into the account the out of plan bending stiffness of slab.
But, ETABS does include the out of plane bending stiffness if you have modelled the slab by using shell elements. So, a factor of 0.7 would overestimate the stiffness of your structure in this case, and will lead to under-design.
If one has used the modifier of 0.35 in ETABS for beams in beam-slab floor system, then what value should be adopted for slab? It should not be 0.25, as this value has been specified for flat plates and flat sab floor system.
If one is using some value of modifier for out of plane bending stiffness on shells, then the share of the bending moment in beams will be reduced accordingly. This approach is correct if one will be providing the reinforcement in column strips of slab. But, if you are providing reinforcement in slab in the direction perpendicular to supports only, i.e. beams, as is the general practice in Pakistan, then you are under-estimating the flexural demand in beams.
Now, there is also a question of factors to be used while deciding the amount of reinforcement required in beams, columns and shear walls.
If you are using factors 0.35 for beams and shear walls, and 0.7 for columns, then you are finding out the demand in members at the point of yielding, and this conforms to the code. But, this also means that the structure might experience unacceptable cracks widths. So, if you are using 0.35 for calculating the demand at strength-level forces, then you should also perform crack-control-check at service-level loads by using the factor of 1.
If you are calculating the strength-level demand with a modifier of 1 for all structural members, after you have decided the location and the number of shear walls with modifier of 0.35, then you are overestimating seismic forces, as you are underestimating the time-period. But, the structural performance will improve.Sat, 29 Apr 2017 06:11:13 +0000Building Joint Displacement/ Drift in EtabsAOA
hope you will be fine
how to calculate building joint displacement from etabs specially for EQ loading and what are the code allowable limits for that .?Thu, 27 Apr 2017 11:17:17 +0000Nonlinear Static Analysis - Applying specific live loadsHello everyone
I'm currently doing nonlinear static seismic analysis of a 4-story building considering post-earthquake damages using ETABS 2015. After applying the aftershock load and performing the second nonlinear static analysis, how can i apply specific additional live loads to the floors? and then perform the third nonlinear static analysis...
I need to find out how many evacuees can enter the building considering the damages obtained by the earthquake main shock and aftershock.
Thank youThu, 27 Apr 2017 04:42:10 +0000Pile Foundation Book Muni BudhuDoes anyone have the soft version of Muni Budhu? If not then any other book which describes the pile foundation topic in such detail as in Muni Budhu.Mon, 24 Apr 2017 07:37:20 +0000Difference between tension controlled and under-reinforced sectionsSalam,
What is the difference between the under reinforced and tension controlled section? Are they same with the exception of strain values of steel.?
Many ThanksSun, 23 Apr 2017 12:16:01 +0000SAGRODS AND SAP2000I have a model from a client to review. There are these horizontal members that are having the P-M Ratio value as greater than 1. Showing that the members are over stressed. Now the client asked me to ignore it, as these elements will be braced by the sag-rods but that they cant be modeled on SAP2000. Is it true that we can't model sag-rods on SAP? If yes, then how can I check that whether these sag-rods will reduce the P-M Ratio of these elements to 1 or not?Thu, 20 Apr 2017 06:21:19 +0000Steel Truss Access BridgeThe attachement is an steel truss access bridge on a earthen dam. What I want to ask is following:
What should be the max. allowable vertical displacement in this case?
How can I design the connections in SAP2000?
Please say whatever you feel like....... constructive criticism. I'm all ears.
New Picture (1).bmp
New Picture (2).bmpTue, 18 Apr 2017 15:40:41 +0000manual mesh vs auto meshRespected members!
how outcomes differ when we do auto and manual mesh?
which is most accurate and preferable?Fri, 14 Apr 2017 09:25:13 +0000STAAD FLOOR LOADSNot a regular user of STAAD and I m really confused by the floor loads. The floor is 3" thick RCC slab. How 2 different floor loads have been applied in dead loads as 50 and 122 psf? The pics are also attached. For 3" slab, shouldn't it be 150*3/12=37.5 psf.Thu, 13 Apr 2017 07:37:02 +0000Interpretation of M11 forces in masonry shell walls in ETABSHi,
I am designing a load bearing masonry wall in ETABS and using IS 1905 code. After viewing the shell forces and stresses, I know that I need to use M11 forces for the design of lintel/horizontal bands to take out of plane lateral loading. But in ETABS i found that the forces are displayed in a unit of KN-m/m (per unit length). How do i convert this value to the total moment for the design of the band. Do I multiply this value by the shell meshing length? Please educate.
Structural Engineer
NepalTue, 11 Apr 2017 09:45:07 +0000waffle slab in etabsAOA
Hope all will be fine
i am facing problem to modal waffle slab in etabs?
A good structure is blessing for others.Mon, 10 Apr 2017 13:17:43 +0000Shop DrawingsAOA.
Can anyone please tell me the rates for preparing a fabrication / shop drawing? I have search on the internet and came to know of 0.5% - 1% of the cost, but I'm not sure about it.Mon, 10 Apr 2017 05:20:16 +0000One day International Seminar (26 April 2017)A two hour session will be held in the Wah campus of CIIT. The attendees will receive a certificate which can be helpful for engineers in matters of PEC-registration.
The speaker will be discussing the topic of performance-based design and evaluation of tall buildings. It is good opportunity for structural engineers to equip themselves with recent advancements regarding the structural analysis and design of tall buildings.
The speaker, Dr. NAVEED ANWAR, who is executive director at AIT Solutions, is not only a Structural engineer, but also has been actively involved in software-development of CSI products such as ETABS, SAP2000 and CsiCol.
Please find the brochure in the attachment for further details.
CPD_Dr Naveed_1.pdfFri, 07 Apr 2017 12:09:14 +0000Foundation Design - Strip footing for a series of column in frame structureHello,
Good evening to everyone. I am designing a strip footing for two storey building. I prepared the model in etabs. I got the support reaction and from that i calculated the strip width = 6'
When i made a Shear diagram using the support reactions (acting downward as point loads) and soil pressure (acting upward as UDL) i got value of critical shear = 108 Kips and one way shear capacity = phi*2*Sqrt(fc')bwd = 68.5 kips for? foundation thickness = 15 inches ... is that right, i mean do we need to calculate one way shear in such cases ? and i got some abnormal kind shear force diagram why is that so? in some point it only goes upward (positive values) - anyway where i am getting wrong?
Bearing capacity = 0.6tsf = 1.32 ksfFri, 07 Apr 2017 07:28:19 +0000slenderness of columnsDear All;
I HAVE A QUESTION REGARDING DESIGN OF COLUMNS IN ETABS ACCORDING TO ACI CODE. IT IS MENTIONED THERE IN SECTION 10.10.2.1 THAT" THE MOMENT INCLUDING THE SECOD ORDER EFFECT IS LIMITED TO 1.4 TIMES THE MOMENT DUE TO FIRST ORDER EFFECT FOR NON SWAY AND SWAY FRAMES". SO HOW CAN I INVESTIGATE THIS IN ETABS?Thu, 06 Apr 2017 14:27:23 +0000