Badar (BAZ)

Let me walk you through a process.I have a task of proportioning members of a RCC building to resistant lateral as well as gravity loads, and intend to use slab, beams, columns and some kind of foundation for the said purpose. I made a model, ran an analysis and found that lateral deflections are so much that they pose structural as well as functional threat. Then I got an idea, i replaced few columns with a member haivng considerably large lateral stiffness. PROBLEM SOLVED, I called it a SHEAR WALL as it has a major contribtuion in resisting lateral loads. Where do you think, gravity loads will go around the vicinity of 'shear wall'? Msonry can also resist shear forces, In fact masonry constructed with good practices can resist upto 100Ksf shear,it is the cyclic loading which creates problem: Ductility is required for that. In rcc, steel and confined concrete caters for that requirement. In short, it is primary reason of choosing particular material or member, that takes the credit/name.

Some engineers may have used this term, but it not a 'standarad term' to describe particular type of structure. Infact, I have only read the term 'bearing wall', which is used for masonry construction; the term is used to differentiate between walls that are part of load transfer mechanism and the walls that are needed for architectural reasons. Every structure has to bear loads. How can a structure stand if it can't bear loads?

Take a look at this link https://wiki.csiberkeley.com/display/etabs/Lost+digit+of+accuracy . One thing that you do is to zoom into that point, reported by ETABS, and see if all the members are connected to that point.

Where will this construction take place? US has reported these values for different cities of the world for the construction of their facilities. I will try to find the document; I once consulted it . Or, you can change code; use UBC 97.

I think, you may be right. But this term is used by the one, formulating a constitutive model to simulate the behaviour of a material under specific loading conditions. For me, who do not and cannot(limited ability) go into such details, makes no difference: both terms define the behaviour of a particular 'node' of a 'finite element' in a mathematical model. raised a good point!

ok, you got confused by confused by 'wording'. I hope you got the concept.

they are springs. Springs are springs and roller are rollers; how are you able to relate these two? you must have seen springs a lot, in motor cycle, cycle...... F = K x. force is directly proprtional to displacement. Roller can 'tranfer' force in one direction.

No difference, as far as I know. I think, the term 'constraint' was used, when people started using numerical anaysis in structural engineering problems.

The term 'spring support' is used to represent a material/structural element whose behavior in only one direction is important,usually linear in nature; it is a mathematical term. The spring elements were used (in mathematical model) in the ealriest attempt of modelling soil under foundation, where only vertical displacements ( settlement) were main corncern for engineer, and these displacements were related to the bearing capacity through modulus of subgrade reaction. Piles can also be modelled by using springs in mathematical behaviour; interaction between poil and soil can be modelled by using spring elements in mathematical model.

You can use summary of results for the eccentricity between center of mass and stiffness. I did not get ur second query. I am also not sure about third query. If you want to validate ur model after running analysis in ETABS; perform some manual checks, such as equation of statics,see if moment diagrams of the members look what they should look like or you can check one of the frames through moment distribution method.

clearly he defined membrane member which can also take compression. What is terminology used for members that can only take tension (i am not talking about cables) like tarpal. This span and thickness of concrete were made possible by the fact that as a circular shell deflects, it creates compression in membrane stresses, thus minimizing the deflection. Did you get the picture of section he might have used for roof slab? I mean there has to something between compression and tension parts of slab.

flexural stiffness of section is ability to attract moments. so cracked section will attract lesser moment as only part of section is available to resist rotation. Do not confuse moment attracting ability( stiffness) of section with its strength. Section with lesser stiffness can have greater strength as it depends upon material strengths, reinforcement and size and shape crossection.

membrane is capable of taking tensile stresses only like our skin or tarpal (urdu word). Word slab used in structural engineering cant be membrane. shall is capable of taking shear and moment. Any thing that can take shear or moment can also take direct tension or compression. plate is shell/slab loaded in its plane like shear wall.

What you do is according to code. There is nothing wrong about it.

Umar is right. Use section modifiers for serviceability checks. This set of modifiers are mentioned in section 10.11.1 of 05 addition which is dedicated to computation of lateral deflections of frame. Remember that code specifications are based on worst case scenario, and these values are worst case scenario for lateral deflections of frame.For elastic analysis of frame it is OK to use gross properties based on rectangular section as it is done in ETABS . We provide rectangular beam section properties in ETABS, but cast in place beam has T section in positive region while rectangular section in negative region, so using rectangular section along entire length compensates for that. Moreover if bottom reinforcement of beam is developed in column, as it is normally done, it increases stiffness of beam in negative region. Amount of reinforcement provided in section also plays its role and we dont know how much reinforcement will be required before starting analysis. Bottom line: it is complex topic and one have to use assumptions. Even if one is using 0.35 and 0.7 factors to size the xsection of member, structure should still stand provided assumptions are uniform through out the analysis, as concrete has this ability to distribute moments according to provided reinforcement.

this can gave you some idea. RJohnson response spectrum analysis.pdf

Do you mean Response spectrum analysis?

In this building shear walls are located at one end and they are not connected to bracing. They will take their share from floor. There is also a steel frame opposite to the group of shear walls, located above the mega truss. Bracing is connected to either outer mega columns or to the steel frame. Its an opinion based on visual observation

yeah it is good

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columns, bracing and shear walls.

there is no inner concrete core in this tower.

Intesa Sanpaolo Tower is under construction in Turin,itlay and it will serve as headquaters for Intesa Sanpaolo bank. It is designed by world-famous architect Renzo Piano. It will have 37 floors + 6 basements on its completion and has a footprint of 1000 square meters. Reason for mentioning it here is the load path used in this building. Only, Six mega columns will transfer entire gravity load of building. Most of the floor load of entire building is transferred to these columns through trusses (only on of them is visible in attached photos) located at about 4 storeys above ground. Laters load are caterred for by steel cable bracing

section 15.7 ACI 318-08.

Every load experienced by superstructure has to be transferred to foundation, where else it can go? One of the important factor in earthquake cases is the soiltype : you cannot put isolated foundation on the soil susceptible to liquefaction. Having said that, Earthquake/wind loads may not have same influence on every structure, depends on type of structure and also construction material. Footing dimensions under the structure with huge gravity loads have lesser effect due to earthquake or wind loads: if soil is not susceptible to liquefaction.