Foundation, Concrete and Earthquake Engineering

Earthquake Requirements for Structural System and Their Detailing

In most cases, in moderate to severe earthquakes some damage will occur in well-designed ductile frames; considerable damage will occur in poorly detailed frames. In order to perform well under earthquake loads the following guidelines must be followed:

1. A moment-resisting frame consists of beams as well as columns

2. Column - flat-slab system rarely perform well in earthquakes

3. Columns must be stronger than beams (in buildings of two or more storeys)

4. Columns must not be too slender (adequate stiffness is required)

5. In general beams in moment-resisting frames must be deeper than gravity-load-only beams

6. Infill walls must be separated from frames

7. Beam-column joints must include ties at close centres across joints (to prevent diagonal shear failure)

8. Concrete strength must be at least 20 MPa, preferably 25 MPa

9. If using high-strength steel ensure it is ductile and follow detailing rules (generally do not weld, thread, re-bend; comply with minimum bend radii)

10. Supervise works to ensure re-bar is not omitted, and details are followed

Special Detailing

a. Beam bar laps must be kept away from potential hinge regions

b. Carry beam primary steel continuously through columns

c. Bend beam bar end to vertical legs

d. Ties are required in all beams and columns

e. Reduce spacing of ties in beams at near column faces

f. Column main bars to be at least D12

g. Column splices to be at mid-height

h. Bend column bar ends into columns

i. Reduce spacing of ties in columns above and below beams (high shear zones)

j. Column ties must continue through joints – closely spaced

k. Tie hooks must be 135º.

Beam-Column Joints in Reinforced Concrete Moment-Resisting Frames

Beam column joints are poorly understood. Inadequate joint shear reinforcement is a common
cause of failure. Failed joints can lead to collapse.

Designers are under pressure to minimise member sizes. The joint becomes too congested with
reinforcing steel. The builder omits some of the steel.

The joint should be stronger than the beam and the column. Design the joint steel before finalising the column size.

Steel Moment Resisting Frames

Similar comments apply to steel moment resisting frames e.g. connections must be at least as strong as members.

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