EARTHQUAKE RESISTANT BUILDINGS (MASONRY)

Prepared by:Raghwinder

2nd Year (Civil)150107082

Introduction Earthquake Resistant Structures• Designed to withstand earthquake• Can’t be entirely immune to damage• Prevents collapsing • Limited loss of functionality

Masonry• Most important construction method• Can resist loads and environmental impact• Fire resistant, Durable, Thermal capacity

General Principles

• Shouldn’t be brittle or collapse suddenly• Resisting Elements• Tied together• Good foundation• Good quality material• Suitably reinforced

Cause of Earthquake

Seismic wavesWhen pieces of crustal rock suddenly slip and move, they release enormous amounts of energy, which then propagates through the crust as seismic waves.

• P waves• S waves

Design Philosophy

• Under minor but frequent shaking, the main members of the buildings that carry vertical and horizontal forces should not be damaged; however buildings parts that do not carry load may sustain repairable damage.• Under moderate but occasional shaking, the main

members may sustain repairable damage, while the other parts that do not carry load may sustain repairable damage.• Under strong but rare shaking, the main members may

sustain severe damage, but the building should not collapse.

Methods of Earthquake Resistant Design

Base Isolation

Energy Dissipation Devices

Designing Masonry Buildings

Masonry has been popular through the ages for its fire resistance, its thermal capacity and its durability.Use of strong mortars, high strength masonry, added reinforcement, improved detailing and the introduction of good anchorage between masonry walls and floors and roofs have enhanced the resistance of masonry to seismic stress.

Masonry MaterialsMasonry Units

Mortar

Concrete Infill

Reinforcing Steel

Figure: Typical bed joint reinforcement

Construction Systems

Unreinforced Masonry

Reinforced Masonry

1. Reinforced hollow units masonry.

2. Reinforced cavity masonry.

Confined Masonry

This is a construction system where masonry structural walls are surrounded on all four sides with reinforced concrete.

Figure: Methods of confining masonry

Walls

• Walls are to be uniformly distributed along each principal axis of the plan.

• The minimum thickness of structural walls should be 240 mm. The total cross-sectional area of structural walls along each of the two axes should not be less than 3% of the gross floor area.

• Adequate foundations and good anchorage between walls and floors are essential.

• Distances between structural walls of reinforced masonry should not be more than 6m; distances in confined masonry should not be more than 8m.

• Partitions should be reinforced with 6 mm ø bars placed at the bed joints with vertical spacing of 600 mm in order to prevent their out-of-plane instability.

General Principles

LintelsLintels should have a minimum of 250 mm bearing length at both ends to prevent local collapse due to crushing of supports during an earthquake. The width of a lintel should not be less than150 mm.In the case of openings larger in area than 2.5 m2, the lintel should be anchored to the tie columns as shown in Figure (a)

If the distance between top of lintel and underside of beam above is less than 60 cm, the two should be united as shown in Figure (b).

Floors and RoofsDuring earthquakes, floors and roofs should act as rigid horizontal diaphragms, which distribute the seismic forces among structural walls in proportion to their stiffness.

Tie BeamsThe function of tie beams is to transfer horizontal shear induced by the earthquakes from the floor and roof to the structural walls. They connect the structural walls with each other and improve the rigidity of the horizontal diaphragms.

Cantilever Slabs and OverhangsThese elements can cause harmful vertical vibration during heavy earthquakes. To reduce this, spans should not exceed those shown on Figure below.

Concluding RemarksMasonry buildings have performed well in several earthquakes worldwide. This construction practice is widely used in many countries and regions for the following reasons: It is based on traditional construction practice; It does not require highly qualified labour (as is the case with RC frame

construction); It has a broad range of applications - it can be used for single-family houses

as well as for medium-rise apartment buildings. Good earthquake performance is based on the following premises: Use of good quality materials, Good quality concrete and masonry construction, and• Simple architectural design.

ThankYou