Earthquake Performance of Brittle Materials and Its Remedy

Performance of Brittle Materials

Brittle building materials such as un-reinforced brickwork, un-reinforced concrete blockwork and un-reinforced concrete should not be used in the primary vertical load and lateral load resisting elements.

Brittle materials tend to be stiff, weak and heavy. This means they attract more lateral loads than flexible elements. Most brittle buildings material carry loads in compression only as they have low tensile strengths.

In moderate earthquakes brittle materials tend to crack; this reduces their resistance to future lateral loads.

In larger earthquakes the brittle building materials usually fail in a sudden manner without giving any warning; after failure, brittle element often cannot sustain gravity loads, meaning the structure usually collapses.

Remedy

In contrast ductile building materials are more flexible; they have the ability to sustain gravity loads without collapse (and to dissipate energy) for several cycles of lateral loads after initial yield.

Mild (and many modern high tensile steels) are ductile. Strengthening connections and columns with steel gives a structure a degree of ductility and often avoids collapse. Well-detailed timber structures are also ductile.

A fully ductile structure, usually of reinforced concrete or structural steel requires specific engineering design and detailing.Where un-reinforced masonry is unavoidable ensure the mortar used is able to accommodate movement. A mortar made from cement, lime and sand can accommodate greater movement than pure cement/sand mortar; the lower strength associated with lime mortars is rarely a problem.