sidnum
Structural
- Jul 14, 2008
- 13
Hi all,
I am doing some masonry panel designs (UK region)and would like to be a bit more "economical" with my design. If I can assume that the base of the panel is fixed, even with the presence of a dpc it would help reduce the amount of windposts and bed reinforcement in my walls. I believe that BS 5628 (COP Masonry) is quite conservative. Why? Well if you try and design walls that will pass the criteria set out in the building regs to the BS it is very hard to ty to get tehm to work. I have included some extracts of codes that I have come across which should be useful.
“CP121 permits the base of a panel to be considered as fixed, despite the presence of a horizontal dpc, provided that the height of the panel exceeds 2.0m”
Ref: External walls design for wind loads, A Haseltine et al. 1984
All our panels are at least 3.5m high
Having spoken to Hyload a dpc manufacturer, I obtained some values for their dpc’s
Hyload Original: flexural strength 0.44N/mm2 and shear strength 0.2N/mm2
Hload Permabit (Bitumen Based): Flexural Strength 0.55N/mm2 and shear 0.31N/mm2
When you compare these to the Values in BS 5628 2005 Part 1, Table 3 Characteristic flexural strength parallel to the bed joints. In our case we are going to be using concrete blocks with compressive strength of 7.3N/mm2, you can see that these values range from 0.1 to 0.25N/mm2 depending on which leaf you consider (140mm inner, 100mm outer).
Consider clause 20.1 of the BS for flexure
“Flexural tension should be relied on at a damp proof course only if the damp proof course consists of a material that has been proved by tests (see DD 86-1) to permit the joint to transmit tension, or if it is constructed with bricks conforming to the requirements of BS EN 771-1 for damp proof course bricks.”
& clause 21.1.2 (c)for shear
“taken as 0.15 N/mm2 for masonry built in mortar strength classes M4 and M2 / designations (iii) and (iv).”
By the way the Hyload DPC’s conform to DD 86-1. Considering the flexural strength and shear values of the masonry and the DPC’s one could argue that the DPC’s are stronger and thus could be treated as continuous!!
Finally if one considers clause 32.2 of the BS
“In the case of cavity construction, continuity may be assumed even if only one leaf is continuously bonded over or past a support, provided that the cavity wall has wall ties in accordance with 25.2.4. Where the leaves are of different thicknesses the thicker leaf is to be the continuous leaf. The load to be transmitted from a panel to its support may be taken by wall ties to one leaf only, provided that there is adequate connection between the two leaves, particularly at the edges of the panels.”
This suggests if the DPC is staggered so that it is not placed on the same course on both leaves of the cavity wall, it may be considered continuous!
I would love to know the thoughts of some more experienced heads on this one , especially examples where you have given fixity to base of a masonry wall panel that has a dpc.
I am doing some masonry panel designs (UK region)and would like to be a bit more "economical" with my design. If I can assume that the base of the panel is fixed, even with the presence of a dpc it would help reduce the amount of windposts and bed reinforcement in my walls. I believe that BS 5628 (COP Masonry) is quite conservative. Why? Well if you try and design walls that will pass the criteria set out in the building regs to the BS it is very hard to ty to get tehm to work. I have included some extracts of codes that I have come across which should be useful.
“CP121 permits the base of a panel to be considered as fixed, despite the presence of a horizontal dpc, provided that the height of the panel exceeds 2.0m”
Ref: External walls design for wind loads, A Haseltine et al. 1984
All our panels are at least 3.5m high
Having spoken to Hyload a dpc manufacturer, I obtained some values for their dpc’s
Hyload Original: flexural strength 0.44N/mm2 and shear strength 0.2N/mm2
Hload Permabit (Bitumen Based): Flexural Strength 0.55N/mm2 and shear 0.31N/mm2
When you compare these to the Values in BS 5628 2005 Part 1, Table 3 Characteristic flexural strength parallel to the bed joints. In our case we are going to be using concrete blocks with compressive strength of 7.3N/mm2, you can see that these values range from 0.1 to 0.25N/mm2 depending on which leaf you consider (140mm inner, 100mm outer).
Consider clause 20.1 of the BS for flexure
“Flexural tension should be relied on at a damp proof course only if the damp proof course consists of a material that has been proved by tests (see DD 86-1) to permit the joint to transmit tension, or if it is constructed with bricks conforming to the requirements of BS EN 771-1 for damp proof course bricks.”
& clause 21.1.2 (c)for shear
“taken as 0.15 N/mm2 for masonry built in mortar strength classes M4 and M2 / designations (iii) and (iv).”
By the way the Hyload DPC’s conform to DD 86-1. Considering the flexural strength and shear values of the masonry and the DPC’s one could argue that the DPC’s are stronger and thus could be treated as continuous!!
Finally if one considers clause 32.2 of the BS
“In the case of cavity construction, continuity may be assumed even if only one leaf is continuously bonded over or past a support, provided that the cavity wall has wall ties in accordance with 25.2.4. Where the leaves are of different thicknesses the thicker leaf is to be the continuous leaf. The load to be transmitted from a panel to its support may be taken by wall ties to one leaf only, provided that there is adequate connection between the two leaves, particularly at the edges of the panels.”
This suggests if the DPC is staggered so that it is not placed on the same course on both leaves of the cavity wall, it may be considered continuous!
I would love to know the thoughts of some more experienced heads on this one , especially examples where you have given fixity to base of a masonry wall panel that has a dpc.
