Sorry this will be a little long.
I am looking at a design where the guardrail system is being substituted for a wire mesh design element that goes between the inside stair stingers on a U-stair with an intermediate landing.
This is important; the wire mesh is to be continuous from the first floor anchorage, up between the stair’s stingers to a connection point at the stair’s roof structure. However, there may have to be a horizontal rated shaft wall cap over the stair before the roof structure is reached. The distance between the stair stinger runs will leave space for the wire mess to pass but between each stinger outside face distance and wire mess face is a 3 ½” gap.
The design is also calling for the wire mesh to be attached at the stair stringers, which slope. This will cause the wire mesh to be more flexible as the distanced between the stringer connections get taller. Therefore, I see some deflection movement in the wire mesh as it’s connection points get farther apart especially at the top last stair run to the 2nd floor’s landing from the intermediate landing. It appears that the guard railing at the landings will be the typical rail system but not between the stair stringers. I am also concerned that the 4” sphere rule must be maintained at ends of the wire mesh (since it is a panel system of a limited width) and the mesh’s abutment close to the landing’s guardrail.
Another concern is how is the contractor going to make the attachment of the wire mesh to the stair stringer as the stingers converge at the intermediate landing? There is only 3 ½” of gap on each side of the mesh to the stinger face. Not much working room for tools.
In the 2012 IBC Section 1607.8 there are sub-sections with the requirements for handrails and guardrails.
I question how this wire mess will comply with the sub-sections loads. There are linear loads and concentrated loads that have to be complied with.
Since the wire mess does not have a typical top rail at 42”, is all the wire mess then nothing but Intermediate Rails?
Will the entire wire mess have to comply with loads as if it was the top rail?
Is any deflection allowed when applying these loads?
Or is the loads looking only for failure at the applied location?
Each load referenced in the sub-sections calls for compliance to Section 4.5.1 in the ASCE 7 document. Of, course I do not have such a document to review. I guess the document addresses the deflection allowed. One thought came to mind if a deflection is allowed. The ends of the wire mesh may deflect enough that will cause the gap between its end and the landing guardrail to be greater thus allowing the passage of a 4” sphere.
Now for the horizontal rated shaftwall question. It is very possible that the weight of this wire mesh system cannot be supported by attachment to the rated shaftwall cap. I question whether or not structural connections can go through the rated cap to the roof structure?
The rated cap is not the finished ceiling. The design calls for a 2’x2’ acoustical tile panel in a suspended lay-in grid which would require the hanger wires to be attached to the rated cap somehow. I suspect that exposed furring strips @ 48” OC and perpendicular to the cap’s joist would be attached to the finished side of the cap at the point of the joist so the suspended ceilings hanger wires would have a place to be attached to without penetrating the rated cap.
A handrail will have to be attached with vertical post from the stair stinger’s flange since wall brackets on this side of the stair will not occur. Of course the handrail’s continuous clearance and allowed vertical interruptions must be in compliance with IBC 1012.4. In Exception 2 there is reference to baluster attachment for the handrail. The vertical post to support the handrail are not really newel posts or other obstructions are they? There is an ADA reference about interruptions along a handrail cannot exceed 20% of the handrail’s length as I recall [ref: 2012 ADA 505.6]. That addresses the handrails connections to something.
Any thoughts on this design?
I am looking at a design where the guardrail system is being substituted for a wire mesh design element that goes between the inside stair stingers on a U-stair with an intermediate landing.
This is important; the wire mesh is to be continuous from the first floor anchorage, up between the stair’s stingers to a connection point at the stair’s roof structure. However, there may have to be a horizontal rated shaft wall cap over the stair before the roof structure is reached. The distance between the stair stinger runs will leave space for the wire mess to pass but between each stinger outside face distance and wire mess face is a 3 ½” gap.
The design is also calling for the wire mesh to be attached at the stair stringers, which slope. This will cause the wire mesh to be more flexible as the distanced between the stringer connections get taller. Therefore, I see some deflection movement in the wire mesh as it’s connection points get farther apart especially at the top last stair run to the 2nd floor’s landing from the intermediate landing. It appears that the guard railing at the landings will be the typical rail system but not between the stair stringers. I am also concerned that the 4” sphere rule must be maintained at ends of the wire mesh (since it is a panel system of a limited width) and the mesh’s abutment close to the landing’s guardrail.
Another concern is how is the contractor going to make the attachment of the wire mesh to the stair stringer as the stingers converge at the intermediate landing? There is only 3 ½” of gap on each side of the mesh to the stinger face. Not much working room for tools.
In the 2012 IBC Section 1607.8 there are sub-sections with the requirements for handrails and guardrails.
I question how this wire mess will comply with the sub-sections loads. There are linear loads and concentrated loads that have to be complied with.
Since the wire mess does not have a typical top rail at 42”, is all the wire mess then nothing but Intermediate Rails?
Will the entire wire mess have to comply with loads as if it was the top rail?
Is any deflection allowed when applying these loads?
Or is the loads looking only for failure at the applied location?
Each load referenced in the sub-sections calls for compliance to Section 4.5.1 in the ASCE 7 document. Of, course I do not have such a document to review. I guess the document addresses the deflection allowed. One thought came to mind if a deflection is allowed. The ends of the wire mesh may deflect enough that will cause the gap between its end and the landing guardrail to be greater thus allowing the passage of a 4” sphere.
Now for the horizontal rated shaftwall question. It is very possible that the weight of this wire mesh system cannot be supported by attachment to the rated shaftwall cap. I question whether or not structural connections can go through the rated cap to the roof structure?
The rated cap is not the finished ceiling. The design calls for a 2’x2’ acoustical tile panel in a suspended lay-in grid which would require the hanger wires to be attached to the rated cap somehow. I suspect that exposed furring strips @ 48” OC and perpendicular to the cap’s joist would be attached to the finished side of the cap at the point of the joist so the suspended ceilings hanger wires would have a place to be attached to without penetrating the rated cap.
A handrail will have to be attached with vertical post from the stair stinger’s flange since wall brackets on this side of the stair will not occur. Of course the handrail’s continuous clearance and allowed vertical interruptions must be in compliance with IBC 1012.4. In Exception 2 there is reference to baluster attachment for the handrail. The vertical post to support the handrail are not really newel posts or other obstructions are they? There is an ADA reference about interruptions along a handrail cannot exceed 20% of the handrail’s length as I recall [ref: 2012 ADA 505.6]. That addresses the handrails connections to something.
Any thoughts on this design?
