As a consulting structural engineer, The University has engaged your services to provide design and assessment for the following structures:
- An existing three (3) storey unreinforced masonry building
- A new reinforced concrete block propped cantilever retaining wall Scale drawings are provided in addition to this
The following design codes are to be used in your analysis:
- 4: 2007 – Structural Design Actions. Part 4: Earthquake actions in Australia
- AS3700: 2018 – Masonry Structures
The existing three (3) storey unreinforced masonry building has the following design parameters:
- Importance Level 2
- Located in Sydney
- Subsoil Class Ce
- Wind loading has been found to be non-critical
- 10mm thick M3 mortar joints (full bedding)
- 230 mm × 110 mm × 76 mm clay units with compressive strength: f’uc = 25MPa
- All load bearing unreinforced masonry walls consist of two (2) skins of masonry (230mm thick total)
- Perimeter walls consist of cavity brick construction comprising a load bearing inner leaf (230mm thick) and a non-load bearing outer leaf (110mm thick). These leaves are separated by a 50 mm cavity and the outer leaf is supported vertically by a shelf angle at slab level and laterally by heavy duty ties connected to the inner
- No damp proof courses or slip joints between unreinforced masonry and concrete floors
- Control joints between plan intersections of all perpendicular walls
- All suspended slabs (level 1, level 2, level 3) 200 mm thick reinforced concrete
- Design loading is as follows for all suspended levels (including the trafficable roof):
- Superimposed dead load gSDL = 1.0 kPa
- Live load q = 3.0 kPa (ψc = 3)
Question 1 – Derivation of seismic actions on building (25%)
- a) Determine the storey seismic weights (Wi) for each suspended level of the building,
hence the seismic weight (Wt) of the entire building. When determining the storey
seismic weights, include the slab selfweight, superimposed dead load, and the weight
of walls, as well as the live load multiplied by the combination factor ψc (see §6.2.2 of
AS1170.4: 2007 for guidance on determining Wt).
- b) Calculate the base shear V for the structure.
- c) Determine the storey seismic force distribution for the building. Present your results
in a diagram like the example shown in Figure 4.
- d) Determine the storey shear force distribution for the building. Present your results in
a diagram like the example shown in Figure 4.
- e) Determined the storey bending moment distribution for the building. Present your
results in a diagram like the example shown in Figure 4.
Question 2 – Compressive capacity of unreinforced masonry (15%)
- a) Determine the ultimate (1.2G+1.5Q) axial force on wall W07 at all levels of the building.
Draw an axial force diagram for this wall (use a similar format to the SFD drawn in
Question 1 part d)).
- b) Check the capacity of wall W07 using “Design by simple rules” in §7.3.3 of AS3700.
Note that you only need to check the capacity of the wall at the critical location i.e.
- c) Suppose that an alternate floor framing arrangement was used for the building with a
300mm wide reinforced concrete beam (so the bearing area is 300mm×230mm)
transmitting an ultimate (already factored) load N* = 250 kN to W07 as shown in
Figure 5. Check the capacity of wall W07 under this loading arrangement. It may be
assumed that the restraint provided to the top of the wall is the same as that provided
by the slab in part (b) above.
Question 3 – In-plane analysis of unreinforced masonry (25%)
- a) For wall W34, determine the dead load, live load for all levels of the building, hence
determine 0.9Wt for W34 at the ground floor of the building (this is the load to be used
for all shear and flexural checks of the wall in accordance with §22.214.171.124 and §126.96.36.199 of
- b) Calculate the relative proportion of seismic forces, hence shears and moments to each
of the walls in the North-South direction (y-direction). You may assume the following:
• The centre of mass and centre of stiffness coincide
• No accidental eccentricity needs is to be considered
• Seismic loading is only applied in the y-direction (North-South direction)
• The floor slabs act as a rigid diaphragm in-plane, with no flexural coupling outof-
plane, that is, the walls act as 12m tall cantilevers.
- c) Using the results from parts a) and b), draw the axial force diagram (for load case
0.9Wt), shear force diagram, and bending moment diagram for wall W34. Note that
although 0.9Wt is taken as the vertical load on the wall, the seismic loads are to be
calculated using Wt (i.e. as previously determined in Question 1).
- d) Check wall W34 for the following:
i. In-plane shear.
ii. Heel tension and toe compression.
Question 4 – Out-of-plane analysis of unreinforced masonry (15%)
- a) Check the out-of-plane capacity of W26 under seismic loading (see §8.3 of
AS1170.4:2007) at the uppermost floor of the building. Assume that the inner (230 mm)
skin of bricks is simply supported at the roof and second floor levels and one vertical
edge is supported laterally by wall W36 (the other vertical edge is not supported). You
may assume that the outer skin of bricks is connected to the inner skin using heavy
duty ties but it is not necessary to check the wall ties. In performing the check assume
that the inertia forces are shared between the two leaves of the wall (see §7.7 of
Question 5 – Reinforced masonry retaining wall (20%)
The retaining wall shown in Figure 6 is fixed to the footing at its base and laterally supported
along its top edge by the attached pavement (that is, it is a propped cantilever). Assume there
is no surcharge loading from the pavement.
- a) Draw the bending moment diagram and shear force diagram for the retaining wall.
- b) Using a block size of 290×190×390 units, design flexural reinforcement (and shear
reinforcement if required) for the retaining wall. You may assume that M4 mortar is
to be used and the units are face shell bedded, the grout compressive strength f’cg =
20MPa and block compressive strength: f’uc = 15MPa. Include the design of starter bars
into the footing but do not design any other reinforcement in the footing.
- c) Provide a neat sketch of your design.
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