unreinforced masonry bending capacity

huangyhg

unreinforced masonry bending capacity?
our australian masonry code (as3700) allows a flexural tensile strength of up to 0.2 mpa (29 psi) for unreinforced masonry during wind and earthquake loading. for other loading you assume zero flexural tensile strength.
what sort of flexural tensile strength does unreinforced masonry actually tend to have?
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i believe the new strength design methods assume no tensile capacity from unreinforced masonry. you must now use rebars to carry your flexural loads. over the past 30 years i have used 10 to 25 psi as a tension value for ungrouted basement walls depending on the mortar type specified.
tom-
allowable flexural tension for unreinforced masonry per aci 530 depends on mortar type and if the stresses are normal or parallel to bed joints. (table 2.2.3.2 in aci 530)
for a basement wall such as cap describes the allowable stress for bending using type m or s mortar, hollow units not grouted is 25 psi (172 kpa).  
my familiarity is with the international building code, and in the current version here under certain circumstances one can use unreinforced masonry to resist seismic loads, but code mandated seismic design loads are higher for an unreinforced system, versus one where rebar are used to help provide resistance.
note also that in the us, even if designed unreinforced the masonry structure is required to have certain minimum amounts of vertical and horizontal steel at openings, corners etc to provide a minimum level of ductility under lateral loads.   dowels and connections that mechanically connect unreinforced structural elements are also specified.   
bottom line is that in us practice you are going to have some steel required even if the structure is designed unreinforced.
bs 5628 gives a range of flexural strengths for masonry, which are related to the direction of bending (parallel or perpendicular to the bed joints), thickness of masonry leaf under consideration, and characteristic compressive strength of unit.
a method also exists to enhance the flexural resistance of the wall due the the beneficial effects of applied vertical dead loads from above.(the weight of imposed snow loads are neglected due to the fact that they may be absent when maximum wind occurrs).
if you post a little more data about your specific masonry leaf, i will get the relevant data from the bs if you wish.
vb
even if there is no mortar bond (eg. at a dpc), a masonry wall under vertical loading always has some flexural capacity, approx equal to the vertical (dead) load x half wall thickness, with the appropriate reductions due to partial safety factor and width of section under compression.
this inherent capacity can be significant, depending on wall weight and thickness.