Beams, Slabs, & Column Design which are not part of the lateral load resisting system 3

[struggle67]

Hi,

I am doing PTBeams and slab design which are not part of the lateral load resisting system of multistorey concrete buildings. In where I practice, all lateral loads (both wind and seismic) are almost always considered to be fully resisted by shear walls and beams & slabs and columns only take gravity loads and no other requirement.

But I am not sure about it. Is there anything that I need to consider for those members (slabs, beams, columns)? Any ductility, detailing, minimum moment capacity requirement? or any vertical component of the seismic force?

If you are familiar with EC8, may I know if there is any clause/statement in EC8?

Thanks and Best Regards,

 

[Tomfh]

In where I practice, all lateral loads (both wind and seismic) are almost always considered to be fully resisted by shear walls and beams & slabs and columns only take gravity loads and no other requirement.

Not sure about EC8, but our Australian concrete code AS3600-2018 has recently cracked down on this approach. Structural elements have to be designed to withstand the earthquake sway, even if the entire lateral load can be carried by other shear walls.

 

[struggle67]

Thanks, Tom,

I think there is a similar requirement in ACI. Should that earthquake sway affect only the columns? Anything to do with horizontal members?

 

[HTURKAK]

Yes, I am familiar with EC 8 and there is a section .. 4.2.2 Primary and secondary seismic members.

Eurocode 8, distinguishes the structural members that have a secondary contribution to earthquake resistance from the primary members . The contribution of ‘secondary’ members to the lateral stiffness and earthquake resistance of the building is not taken into account in the analysis for the seismic action. Only ‘primary’ members are designed and detailed for earthquake resistance with
the rules of Eurocode 8. However, the secondary members SHALL be designed to maintain support of gravity loads under the most adverse displacements and deformations imposed on them in the seismic design situation .

The designer is free to choose which members, will be assigned as ‘secondary’, with two restrictions specified in Eurocode 8:
1.The total contribution to lateral stiffness of all secondary seismic members should not exceed 15% of that of all primary seismic members
2. The characterisation of some of members as ‘secondary’ not allowed to change the classification of the structure from irregular to regular.

Pls look to the requirements for DUAL SYSTEMS and Resistance of horizontal diaphragms, Design provisions for diaphragms.

If this is real question , pls provide some details to get specific responds.

 

[Enhineyero]

I am doing PTBeams and slab design which are not part of the lateral load resisting system of multistorey concrete buildings. In where I practice, all lateral loads (both wind and seismic) are almost always considered to be fully resisted by shear walls and beams & slabs and columns only take gravity loads and no other requirement.

This is a common approach. Note that detailing plays a role here. Also, I look at the relative stiffness of members when deciding if dual systems is a more appropriate lateral load resisting system. In most cases, shear walls are very rigid that beam/column frames barely attract lateral loads.

Also not too familiar with EC8. code tells us to consider forces due to inter-story drift, for most buildings I wouldn't be too concerned about this as inter-story drifts between floors are small and will produce very little addition moments. But if you are designing tall buildings, then this should be looked at more closely.

 

[Agent666]

Definitely design for the most adverse compatibility deformations as others have noted. ACI421 series of standards contain some good information on the design and checking of the column/slab interfaces for this deformation, of which the concepts could be applied in a Eurocode sense.

One of the keys aspects to recognise is detailing the interface to achieve a level of ductile failure in punching shear. This prevents the brittle failure normally associated with a punching shear failure.

 

[struggle67]

Hi Thanks HTURKAK, Enhineyero, and Agent666

Your replies really enlightened me.

I am more concerned about the beam and slab because they are my responsibility (PT Specialist). I am just curious about columns and walls and for my knowledge. Seems like on my part I only have to worry about column/slab interface especially punching shear.

I will go and study all the references that you guys mentioned EC8 4.2.2 and ACI421. Hopefully, I won't need to disturb you all again with those details.

Thanks