by

PROFESSORAPPLIED MECHANICS DEPARTMENT

L D COLLEGE OF ENGINEERINGAHMEDABAD – 380 015.

Construction of Cyclone Resistant Buildings

(25-06-2020)

• Earthquake

• Cyclone

• Flood

• Fire

• Landslides

• Liquefaction

• Tsunami

Effect of Disasters

• Fundamental of Designing CycloneResistant Buildings

Engineered and Non-Engineered

• Planning aspects of a building incyclone prone areas

CSS Personal\Cyclone ResistantConstruction\Damages due toCyclone.mp4

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

Lateral forces create discomfort tostructures – Wind & Earthquake

Dead Load + Live Load +Wind or EQ Load DL + LL + WL or EQ

Earthquake ForceF = mass x acceleration

= ma

Wind ForceF = 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 buildingand the roof, the better is theperformance of the house. Lighter roofwould not induce as much load on thewalls, and the walls would be able totransfer the loads easily during anearthquake.

On the other hand, during a cyclone,heavier the roof, the better is theperformance of the house. It would resiststrong 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 Vz2

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 mostimportant factor for better performance ofbuildings subjected to cyclones.

Recommendations to improve performance ofnon-engineered building with minimumconstruction cost :

1. Symmetrical building for balanced distributionof forces in the structure.

2. Restrict height of buildings to one/two storeys

3. Ensure that lightweight floors and roofs aresecurely fastened to the walls.

4. Lightweight roofs should have a hipped shape(sloping in four directions) rather than a gableshape (sloping in two directions). Lightweightroofs should be not less steep than 20 degrees(generally, the steeper the better up to about30 degrees) to improve wind resistance.

5. Lightweight roofs should have minimumoverhangs at the eaves. In fact is would bebetter to have no overhangs and to introducea parapet. The need to shade windows anddoors from sun and rain may be met byseparate 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 wherethe loss of roofs has triggered thetotal destruction of un-reinforcedmasonry walls.

• The design of low rise reinforcedconcrete frames is usually controlledby the seismic hazard. But care stillneeds to be taken to ensure that theconcrete frames can accommodatethe wind forces. There have been afew 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 ROOFCORRUGATED 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

FOUNDATIONS

THE REINFORCEMENT IN THE CONCRETE BLOCK

WALL TIED TO THAT OF THE FOUNDATION.

FOUNDATIONS

Apart from roofs, the elements requiring themost attention are windows and doors. Sadly,these are often neglected even when buildingsare formally designed by professionals. Glasswindows and doors are, of course, veryvulnerable 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 withstrong bolts or braces and to fix door andwindow frames firmly to the walls.

WINDOWS

LocationThe location of the building is important. Weoften have little choice in the matter, perhapsbecause of financial constraints. It is as well,therefore, to recognize when a building is beinglocated in a more vulnerable area. The rationalresponse would be to build a stronger-than-normal house. Such vulnerable areas includeopen-ended valleys, which act as funnels for thewind, and exposed hill crests. Both conditionslead to acceleration of wind speeds with thecorresponding 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 determiningthe performance of buildings in cyclones. Simple,compact, symmetrical shapes are best. The square planis better than the rectangle. The rectangle is better thanthe L-shaped plan. This is not to say that all buildingsmust be square.

Even more important than plan shape is roof geometry.For lightweight roofs it is best that they be of hippedshape (sloping in all four directions, usually), steeplypitched (25 to 30 degrees), with little or no overhangs atthe eaves (with parapets if possible) and with ridgeventilators where these are practicable.

DESIGN OF THE HOUSE

RELATIVE PLANNING

References•A manual on Safe Construction Techniques prepared aspart of the OAS/USAID Caribbean Disaster MitigationProject (CDMP)

•CYCLONE RESISTANT BUILDING ARCHITECTURE by GoI –UNDP, Disaster Risk management Programme

•Wind Storms, Damage and Guidelines for MitigativeMeasures, Document No. :: IITK-GSDMA-Wind03-V3.0Final Report-

.

Thank you