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1
- #1
COEngr
Structural
- Sep 17, 2013
- 3
I'm currently doing some work for the owner of an Unreinforced Masonry (URM) building located in Portland, OR. Running through the Tier 1 checks (similar to the Tier 1 checks of the ASCE 31-03 previously), the building has several deficiencies as expected including In-Plane and Out-of-Plane actions. Moving on to Tier 2 to address these deficiencies, I'm stumped by two issues and don't have clear guidance as this is a very new code document.
1. Section 11.3.2.2.2 addresses the "In-Plane Bed-Joint Sliding Strength" and provides values for bond + friction and friction only. Section 11.3.2.3.1 then indicates that only friction can be used for Life-Safety Performance objectives. Is there any way to use tested values from the building to demonstrate that the joint doesn't shear and still has bond strength even after a seismic event? Or are you forced to rely on half the dead load sitting on the pier as your bed joint resistance?
2. Section 11.3.3 addresses Out-of-Plane actions and indicates that "URM walls shall not be analyzed for out-of-plane actions using the linear static procedure (LSP) or nonlinear static procedure (NSP) prescribed in Chapter 7." This is similar to section 7.3.3 of ASCE 41-06. My question is, what are people doing for a dynamic analysis of URM buildings with flexible diaphragms? RAM model? Most modal analyses don't deal with the inertial forces on the walls, but instead group mass/force at nodes. So if static procedures aren't permitted, what does a dynamic analysis look like for a building of this type? If I can show that the wall doesn't crack in a pinned-pinned, static loading condition (fb<fte) using expected tensile strength of the masonry, wouldn't a dynamic analysis only reduce the demands on the wall by "softening" the diaphragm reaction into a spring?
If anyone has any resources for how to apply this new code at all but ESPECIALLY for URMs, I would be very grateful.
1. Section 11.3.2.2.2 addresses the "In-Plane Bed-Joint Sliding Strength" and provides values for bond + friction and friction only. Section 11.3.2.3.1 then indicates that only friction can be used for Life-Safety Performance objectives. Is there any way to use tested values from the building to demonstrate that the joint doesn't shear and still has bond strength even after a seismic event? Or are you forced to rely on half the dead load sitting on the pier as your bed joint resistance?
2. Section 11.3.3 addresses Out-of-Plane actions and indicates that "URM walls shall not be analyzed for out-of-plane actions using the linear static procedure (LSP) or nonlinear static procedure (NSP) prescribed in Chapter 7." This is similar to section 7.3.3 of ASCE 41-06. My question is, what are people doing for a dynamic analysis of URM buildings with flexible diaphragms? RAM model? Most modal analyses don't deal with the inertial forces on the walls, but instead group mass/force at nodes. So if static procedures aren't permitted, what does a dynamic analysis look like for a building of this type? If I can show that the wall doesn't crack in a pinned-pinned, static loading condition (fb<fte) using expected tensile strength of the masonry, wouldn't a dynamic analysis only reduce the demands on the wall by "softening" the diaphragm reaction into a spring?
If anyone has any resources for how to apply this new code at all but ESPECIALLY for URMs, I would be very grateful.
