Shear Wall Openings

[abusementpark]

I have a question about concrete shear box walls.

It is common for concrete shear boxes to be used as elevator shafts in multi-story building. Unlike single, isolated shear walls, the walls in the box that are perpendicular to the load are used as flanges and they take the compression/tension forces. The walls in the box that are parallel to the load must take the shear, similar to a beam web.

My question is with regards to the walls that are parallel to the load and must take the shear force. How do you analyze what is happening with the shear forces around the openings? At each floor there has to be openings for elevator or stair entrances.

What do engineers typically do analyze what is happening and how these local regions need to be reinforced?

 

[rowingengineer]

What you want is a Coupled shear wall, here is an description by others:

"a coupled shear wall is a continuous wall with vertical rows of opening created for windows and doors, coupled by beams that interconnecting the blade walls across the openings. The connecting beams are referred to as coupling beams. It may be shallow or deep beam type, however the most common type used is a deep beam type. Coupling beam has adequately strong and stiff under elastic loading, ductile and able to dissipate energy under inelastic loading.

The coupling beams in between are actually constraint the walls to deflect similarly and will be subjected to flexural and shear combined. When shear blade walls are interconnected by a system of beams or slabs, the total stiffness of the system exceeds the summation of the individual wall stiffness because the connecting slab or beam restraints the individual cantilever action by forcing the system to work as composite unit. This type of system can used economically to resist lateral loads in buildings up to about 40-stories."

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[hokie66]

The most common type of core is probably where you have two banks of elevators, one on each side of an elevator lobby. The walls behind the elevator and the returns on each end form a 'C' or channel shape, which provides a lot of stiffness in the direction parallel to the back wall. The front wall, where the elevator doors occur, is usually ignored, as there is little if any structure left.

In the other direction is where the coupling beams occur which RE refers to above. These beams have the effect of making the channels on each side work as push-pull members, with the coupling beams up the height of the building serving to transfer the load across. The design and detailing of these beams is a critical element in high rise cores, as the reinforcement is congested where the beam bars enter the wall.

 

[ishvaaag]

I would say that the more important thing when analyzing some shearwall of significant proportions is something rarely insisted upon: that the analysis be made taking unto account the P-Delta effects for some plausible degraded state of stiffness of the shearwall, compatible with the results of such analyses.

Shearwalls may well work in single curvature along the very tall heights of important buildings, or if in double curvature, the lengths between inflection points can still be awesome. The weak axis bend buckling of the proportionally thin shearwalls then becomes paramount, and also bracing against it. So you need to prove yourself that this overall bend buckling behaviour has been properly counteracted upon by other concomitant structural schemes present, and you do it by analyzing with P-Delta and seeing drift deformation converge to acceptable limited values i all directions.

AFTER that you may start thinking of shearwall panels or elements in what you will have to follow the stresses present, and if taking the form of some beamcolumn or beam, also follow the recommendations for such for the specific use.

 

[80smetalfm]

Location and size of the Openings in the shearwalls is the major issue here. Keep all openings within the centre of shearwall away from your compression zones.

Do you use ETABS? Modelling these "parallel" zone as spandrells and detail as a coupled shearwall would be the answer. If you dont use ETABs or similar programs the calcs involved in this excercise would take some time to do. Depending on your "lintel depth" you would be going from either a hori beam coupled beam or an "X" type detail would be required at the worst case of which would require some SW space/room!

Keep your openings less than 5% of overal gross face area.

 

[vandede427]

in coupled shear walls you will have very high shear and negative moments in the beams over the openings. don't ignore these.