Construction of Cyclone Resistant Buildings (25-06-2020) by - - PowerPoint PPT Presentation

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PROFESSOR APPLIED MECHANICS DEPARTMENT L D COLLEGE OF ENGINEERING AHMEDABAD – 380 015.

Construction of Cyclone Resistant Buildings

(25-06-2020)

• Earthquake
• Cyclone
• Flood
• Fire
• Landslides
• Liquefaction
• Tsunami

Effect of Disasters

• Fundamental of Designing Cyclone

Resistant Buildings Engineered and Non-Engineered

• Planning aspects of a building in

cyclone prone areas

CSS Personal\Cyclone Resistant Construction\Damages due to Cyclone.mp4

Design Loads

• Dead Load
• Live Load
• Wind Load
• Earthquake Load
• Many other types of loads

Lateral forces create discomfort to structures – Wind & Earthquake

Dead Load + Live Load +Wind or EQ Load

DL + LL + WL or EQ

Earthquake Force F = mass x acceleration = ma Wind Force F = Intensity of wind x Area of Obstruction Torsional Rigidity

Cyclone Resistant Design

• No damage condition

Earthquake Resistant Design

• Damage allowed but no collapse

During an earthquake, lighter the building and the roof, the better is the performance of the house. Lighter roof would not induce as much load on the walls, and the walls would be able to transfer the loads easily during an earthquake. On the other hand, during a cyclone, heavier the roof, the better is the performance of the house. It would resist strong loads due to the wind pressure, hold itself and the house in place.

Cyclones are among the most destructive natural phenomena. The impact from cyclones extends over a wide area, with strong winds and heavy

• rains. However, the greatest damage to

life and property is not from the wind, but from secondary events such as storm surges, flooding, landslides and tornadoes.

• Design wind speed Vz

= Vb k1 k2k3

– Vz

–Vb

= design wind speed at any height z in m/s = basic wind speed in m/s

–k1 = probability factor (risk coefficient) Table 4 –k2 = terrain, height and structure

size factor

–k3 = topography factor

Design wind pressure

pz = 0.6 V

z 2

Wind Speed & Damage relation

Category m/s mph Damage

HC1 HC2 HC3 HC4 HC5 33 - 42 43 - 49 50 - 58 59 - 69 > 69 74 - 95 96 - 110 111 - 130 131 - 155 > 155 Minimal Moderate Extensive Extreme Catastrophic

Non-Engineered Building – Vulnerable Engineered Building

• Well designed – Perform Satisfactory
• Poorly designed - Vulnerable

HOW HIGH WINDS DAMAGE BUILDINGS ?

• The walls of the building are pulled apart by

winds moving swiftly around and over the building

• This creates suction on the walls and roof,

effectively causing the equivalent of an explosion

Structural configuration is the single most important factor for better performance of buildings subjected to cyclones. Recommendations to improve performance of non-engineered building with minimum construction cost :

• 1. Symmetrical building for balanced distribution
• f forces in the structure.
• 2. Restrict height of buildings to one/two storeys
• 3. Ensure that lightweight floors and roofs are

securely fastened to the walls.

• 4. Lightweight roofs should have a hipped shape

(sloping in four directions) rather than a gable shape (sloping in two directions). Lightweight roofs should be not less steep than 20 degrees (generally, the steeper the better up to about 30 degrees) to improve wind resistance.

• 5. Lightweight

roofs should have minimum

• verhangs at the eaves. In fact is would be

better to have no overhangs and to introduce a parapet. The need to shade windows and doors from sun and rain may be met by separate canopies.

• Timber Houses
• Steel Frames
• Masonry Houses
• Reinforced Concrete Frames

• Light weight structure

Steel Portal Frame Building with Light Roofing System

• These are usually safe in cyclones.

There are countless examples where the loss of roofs has triggered the total destruction

• f

un-reinforced masonry walls.

• The design of low rise reinforced

concrete frames is usually controlled by the seismic hazard. But care still needs to be taken to ensure that the concrete frames can accommodate the wind forces. There have been a few isolated examples where, ignoring this, has led to disaster.

Components failure

• Roof Sheeting
• Roof Tiles
• Rafters
• Connections
• Walls
• Foundation
• Windows & Doors

Roofs that aren’t anchored properly can get uplifted during a cyclone/windstorm. Light weight temporary shelters, which are not held properly, may blow away. CGI sheets/tiles could blow away if not anchored well.

The pressure of the wind builds up on the ceiling inside the house to such an extent that the clay tiles are blown away.

THE ROOF

CORRUGATED GALVANIZE SHEETS ARE GAUGED BY NUMBERS. THE HIGHER THE NUMBER THE THINNER THE MATERIAL.EXAMPLE 24 GAUGE GALVANIZE IS SUPERIOR TO 28 GAUGE. HOW DOES ROOF SHEETING FAIL IN CYCLONES?

ROOFING MATERIALS GALVANIZED SHEETS

IF GALVANIZED SHEETS ARE USED 24 GAUGE IS RECOMMENDED IF YOU MUST USE 26 GAUGE WHICH IS THINNER, THIS IS HOW TO HOLD YOUR SHEETING TO THE ROOF STRUCTURE.

At ridges, eaves and overhangs - fixings every two (2) corrugation. All other locations, fixings every three (3) corrugation. Maximum spacing.

THE ROOF

THE WALLS

THE WALLS MUST BE SECURELY TIED TO THE FOUNDATION TO PREVENT THE WIND FORCES LIFTING UP THE ENTIRE BUILDING OR BLOWING IT OVER.

Foundation (too small for light weight building) pulled completely out of ground

Box action give very high integrity FOUNDA TIONS

THE REINFORCEMENT IN THE CONCRETE BLOCK WALL TIED TO THAT OF THE FOUNDATION.

FOUNDA TIONS

Apart from roofs, the elements requiring the most attention are windows and doors. Sadly, these are often neglected even when buildings are formally designed by professionals. Glass windows and doors are,

• f

course, very vulnerable to flying objects. There are only two solutions:

• use impact-resistant glass (very expensive)
• cover the glass with storm shutters

Attention must also be paid to secure doors with strong bolts or braces and to fix door and window frames firmly to the walls.

WINDOWS

Location The location of the building is important. We

• ften have little choice in the matter, perhaps

because of financial constraints. It is as well, therefore, to recognize when a building is being located in a more vulnerable area. The rational response would be to build a stronger-than- normal house. Such vulnerable areas include

• pen-ended valleys, which act as funnels for the

wind, and exposed hill crests. Both conditions lead to acceleration of wind speeds with the corresponding increase in damage potential.

BASIC DESIGN CONSIDERATIONS

• When choosing a site for your home…

BASIC DESIGN CONSIDERATIONS

• When choosing a site for your home…

A house is best built on a flat firm site provided it is well drained. If your lot is on a slope don’t place the house like this unless it is properly anchored. The wind and water can dislodge the house. Cut and fill is a common means of leveling a house site. Avoid building on the fill. Foundation should be on solid

• ground. This house is safer

, cut into the side of the hill.

Shape is the most important single factor in determining the performance of buildings in cyclones. Simple, compact, symmetrical shapes are best. The square plan is better than the rectangle. The rectangle is better than the L-shaped plan. This is not to say that all buildings must be square. Even more important than plan shape is roof geometry. For lightweight roofs it is best that they be of hipped shape (sloping in all four directions, usually), steeply pitched (25 to 30 degrees), with little or no overhangs at the eaves (with parapets if possible) and with ridge ventilators where these are practicable.

DESIGN OF THE HOUSE

RELATIVE PLANNING

References

• A manual on Safe Construction Techniques prepared as

part of the OAS/USAID Caribbean Disaster Mitigation Project (CDMP)

• CYCLONE RESISTANT BUILDING ARCHITECTURE by GoI –

UNDP, Disaster Risk management Programme

• Wind Storms, Damage and Guidelines for Mitigative

Measures, Document No. :: IITK-GSDMA-Wind03-V3.0 Final Report-

.

Thank you