Earthquake Resistant Design Techniques

EARTHQUAKE RESISTANT CONSTRUCTION DETAILS

Various types and construction details of foundation, soil stabilization, retaining walls, underground and overhead tanks,

staircases and isolation of structures

UTKARSH SHAKYA (11601)

SAHIL KAUNDAL (11602)B.Arch. ,7th Sem.

National Institute of Technology Hamirpur

1

CONTENTS

1. Why earthquake resistant construction details?? (Introduction)

2. Various types and construction details of foundation.

3. Soil stabilization

4. Retaining walls

5. Underground and overhead tanks

6. Staircases and isolation of structures

2 AR-414 Earthquake Resistant Building Design Earthquake Resistant Construction Details

Why Earthquake resistant construction??

India is a large country. Nearly two thirds of its area is earthquake prone. A large part of rural and urban buildings are low-rise buildings of one two three storeys. Many of them may not be adequately designed from engineers trained in earthquake engineering. Most loss of life and property due to earthquakes occur due to collapse of buildings. The number of dwelling units and other related small-scale constructions might double in the next two decades in India and other developing countries of the world. This amplifies the need for a simple engineering approach to make such buildings earthquake resistant at a reasonably low cost.



Various types and construction details of foundation




Types of Foundations:

Stone Masonry Foundation


Brick Masonry Foundation


Concrete Block Masonry Foundation

- In case of loose soil, provide some nominal reinforcement in foundation bed concrete.- If stone soling is used under foundation reduce the thickness of foundation strip to 3”.- The vertical steel bars indicated in the foundations are to be provided at corners andjunction of walls as explained in the later sections.


FoundationsOne of the most frequent causes of deterioration of the walls of a house is their directcontact with the ground humid thus making them vulnerable in the event of anearthquake.

Example: ground sloping towards the wall, unstable and poor quality foundations andwall bases, prone to settling due to the effect of humidity and the inferior quality of theground.


Alternative 1: Cleaning & DrainageIf after an earthquake the wall has cracks in certain sectionsand the bricks are in a satisfactory state we must eliminate theearth which covers the wall base, and level out the ground aminimum of 100mm below the wall base.

Alternative 2: Demolition & ReconstructionIf after an earthquake the base of the wall has become loose,if there are cracks in the entire wall and sinking which makesthe wall unstable and dangerous, we must then: Dismantle itafter propping it up and build a new wall from the foundations.


WOOD FRAMED WALLSFoundationsTimber construction shall preferably start above the plinth level, the portion belowbeing in masonry or concrete. The superstructure may be connected with the foundationin one of the two ways:A) The superstructure may simply rest on the plinth masonry, or in the case ofsmall buildings of one storey having plan area less than 50 sq.m., it may reston firm plane ground so that the building is free to slide laterally during groundmotionB) The superstructure may be rigidly fixed into the plinth masonry or concretefoundation as shown in fig.13.1 or in case of small buildings it may be fixed tovertical poles embedded into the ground.

Details of connection of column with foundation


Wall Footings

Pier Post and Column Footings


SHALLOW FOUNDATION - Spread Footings: Single footing, Stepped footing, Sloped footing, Wall footing, Grillage foundation.

Spread footings are those which spread the super-imposed load of wall or column over a larger area. Spread footings support either a colunm or wall. Spread footings may be of the following kinds:

(i) Single footing [ Fig. 2.2(a)] for a column(ii) Stepped footing [ Fig. 2.2(b)] for a column(iii) Sloped footing [ Fig. 2.2(c)] for a column(iv) Wall footing without step [ Fig. 2.3(a)] (v) Stepped footing for wall [ Fig. 2.3(b)] (vi) Grillage foundation [ Fig. 2.4]

http://www.abuildersengineer.com/2012/10/shallow-foundation-spread-footings.html


Fig. 2.2 SPREAD FOOTINGS FOR COLUMNS.

Fig. 2.2 (a) shows a single footing for a column, in which the loaded area (b x b) of the column has been spread to the size B x B through a single spread. The base is generally made of concrete. Fig. 2.2 (b) shows the stepped footing for a heavily loaded column, which requires greater spread. The base of the column is made of concrete. Fig. 2.2 (c) shows the case in which the concrete base does not have uniform thickness, but is made sloped, with greater thickness at its junction with the column and smaler thickness at the ends.

FIG. 2.3 SPREAD FOOTING FOR WALL : STRIP FOOTING.

Fig. 2.3 (a) shows the spread footing for a wall, consisting of concrete base without any steps. Usually, masonry walls have stepped footings as shown in Fig. 2.3 (b), with a concrete base


FIG. 2.4 GRILLAGE FOUNDATION.Fig. 2.4 shows a steel grillge foundation for a steel stanchion carrying heavy load. It is a special type of isolated footing generally provided for heavily loaded steel stanchions and used in these locations where bearing capacity of soil is poor. The depth of such a foundation is limited to 1 to 1.5 m. The load of the stanchion is distributed or spread to a very large area by means of two or mor tiers or rolled steel joints, each layer being laid at right angle to the layer bellow it. Both the tiers of the joists are then embeden in cement concrete to keep the joists in position and to prevent their corrosion.The detailed method of construction has benn explained in 3.6 Grillage foundation is also constructed of timber beams and planks (Fig. 3.12 and 3.13)

Ground and Soil Stabilisation

General problems of ground instability include:

• Landslip• Surface flooding and soil erosion• Natural caves and fissures• Mining and quarrying• Landfill• Natural geological variation – faults,

changes in geology – differential settlement

Improving the ground

• There are a number of different methods that can be used to increase the strength and stability of the ground.

Ground stabilisation

• Dynamic compaction• Vibro compaction - Vibro displacement • Vibro flotation - high pressure water jets (improves

penetration of hard substrates)• Pressure grouting • Surcharging• Geotechnic membranes• Soil modification and stabilisation

Dynamic compaction

• This involves dropping heavy weights onto the ground.

• The weight causes the ground to compact.

Dynamic compaction

• Ground is consolidated by repeatedly dropping dead weights and specially designed tampers

• Weights include: Flat bottomed and cone tampers• Traditional weights are flat bottomed with cable• Modern systems use cones with guide rails• Dynamic compaction is suitable for granular soils,

made-up and fill sites• Using dynamic compaction bearing capacities of 50

to 150kN/m2 can be achieved

Dynamic compaction

Typical weight (mass) 7-11 tonnes

Tamer drops and exerts known impact energy on strata

Pass 2 Pass 2 Zone compacted 2nd Pass

Zone compacted 1st Pass

Pass 1 Pass 1

Zone compacted 3rd Pass

Sound strata

Pass 1 and pass 2

Pass 3

50 – 150 kN/m2 Typical bearing capacity

Required treatment depth

Typical cone type tampers (adapted from www.roger-

bullivant.co.uk) Long cone

Flower pot cone

Multiple point cone

Used for densifying deep layers of strata

Consolidates strata closer to the surface

Typical weight (mass) 7-11 tonnes

2.5m

Traditional weight

10 – 20 tonnes Energy does not penetrate the ground as much as the cone weights

Dynamic compaction rig

Vibro compaction or displacement

• Vibrating rods are forced into the ground causing the surrounding ground to compact and consolidate.

Vibro compaction or vibro displacement

• Vibrating mandrels (poker, shaft or rod) penetrates, displaces and compacts the ground.

• Void Created is filled with stone and recompacted• Produces stone columns in the ground, compacts

surrounding strata enhancing the ground bearing capacity and limiting settlement

• Typical applications include support of foundations, slabs, hard standings, pavements, tanks or embankments.

Vibro compaction - continued

• Used in soft soils, man made and other strata, can be reinforced to achieve improved specification

• On slopes it can limit the risk of slip failure. • Ground bearing capacities, for low to medium rise

buildings and industrial developments, is in the region of 100kN/m2 to 200kN/m2.

• Improved ground conditions may allow heavier loads to be supported.

• Used in granular and cohesive soils

Benefits of vibro-compaction

• Buildings can be supported on conventional foundations (normally reinforced and shallow foundations).

• Work can commence immediately following the vibro displacement. Foundations can be installed straight away.

• The soil is displaced. No soil is produced.• Contaminants remain in the ground – reduces disposal

and remediation fees.• Economical, when compared with piling or deep

excavation works.• Can be used to regenerate brownfield sites• Can use reclaimed aggregates and soils.

Vibrofloatation

• Vibro floatation uses a similar process to vibro compaction

• Water jets at the tip of the poker • Water jets help the vibrator penetrate hard

layers of ground • Major disadvantage is that the system is

messy and imprecise, thus rarely used

Vibro displacement - Typical sequence

2. As the mandrel drives into the ground the soil is displaced (surrounding granular soil is compacted.

1. A grid is marked out and the vibrating mandrel (poker) is inserted to the required depth

Vibro displacement - Typical sequence

3. Having reached the engineered depth the mandrel is withdraw and hardcore is placed up to the first level. The hardcore is built up in layers of 0.3 to 0.6m. The mandrel is inserted into the hardcore, it penetrates and compacts each layer before the next load of hardcore is placed

Rigs weighs 14 – 55 tonnes

4. By compacting in layers and reintroducing the cone mandrel a dense stone column is constructed.

Mandrel positioned ready to compact and displace

Ground displaced

Ground compacted void remains

Void filled with stone

Hardcore is repeatedly displaced and compacted

Grouting

• Grouting may be used to fill the voids in the ground increasing the strength of the ground.

Pressure grouting

• In permeable soils, pressure grouting may be used to fill the voids.

• Holes drilled using mechanically driven augers.• As the auger is withdrawn cement slurry is forced

down a central tube into the bore under pressure. • Pressures of up to 70,000 N/mm2 can be exerted by

the grout on the surrounding soil. • Slurry contains cementious additives, e.g. pulverised

fuel ash (pfa), microsilica, chemical grout, cement or a mixture.

Soil modification and stabilization

• Machines are available that can break-up the ground, mix the ground with new cementious material and improve the ground quality.

Soil modification and recycling

• Additives used in soil stabilisation increase the strength better, improve compacted and maximise bearing capacity and minimise settlement.

• The technique can be used to provide stabilised or modified materials for earthworks, or may be used to provide permanent load transfer platforms or hard standings.

• Can be used to treat and neutralise certain contaminants or encapsulate the contaminants, removing the need for expensive removal and disposal.

Soil modification, stabilisation and recycling machine

Milling and mixing chamber

Working direction

Unstable soil Stable or modified soil ready for compaction

Schematic of soil modification and mixing chamber

The milling and mixing rotor breaks down soil and mixes the soil and additives

Hopper and cellular wheel sluice spread lime or cement or other additive

Variable milling and mixing chamber.

Soil mixture with reduced water content – ready for compaction

Working direction

Soil modification and stabilization rig

www. roger-bullivant.co.uk

Soil modification and stabilization plant



Soil modification and stabilization plant


Surcharging

• This involves placing heavy loads on the ground for long periods of time.

• Over time the ground will compact.• Surcharging is time consuming and ties up the land• Can be used if long lead-in time available• Can be used on roads• May be used on investment land (land bank). The

increase in strength will increase the value of the land.

Surcharging

• Excavated material, quarried stone or other heavy loads.

• Settlement and compaction period 6 months to a few years.

• For economics the surcharging acts as a temporary storage facility

Geotechnical membranes

• Geotechnical membranes provide a sheet of reinforcing material that can be added to the ground. This increases the stability and tensile strength of the ground.

Geotecnic membrane

Geotechnical membranes

• Natural• Plastic manmade• Built up in layers compacted between ground

hardcore• Sheets, fibres and strips

59

5. Field Compaction Equipment and Procedures

60

5.1 Equipment

Smooth-wheel roller (drum) • 100% coverage under the wheel

• Contact pressure up to 380 kPa

• Can be used on all soil types except for rocky soils.

• Compactive effort: static weight

• The most common use of large smooth wheel rollers is for proof-rolling subgrades and compacting asphalt pavement.

Holtz and Kovacs, 1981

61

5.1 Equipment (Cont.)

Pneumatic (or rubber-tired) roller • 80% coverage under the wheel

• Contact pressure up to 700 kPa

• Can be used for both granular and fine-grained soils.

• Compactive effort: static weight and kneading.

• Can be used for highway fills or earth dam construction.


62


Sheepsfoot rollers • Has many round or rectangular shaped protrusions or “feet” attached to a steel drum

• 8% ~ 12 % coverage

• Contact pressure is from 1400 to 7000 kPa

• It is best suited for clayed soils.



63


Tamping foot roller • About 40% coverage


• It is best for compacting fine-grained soils (silt and clay).



64


Mesh (or grid pattern) roller • 50% coverage


• It is ideally suited for compacting rocky soils, gravels, and sands. With high towing speed, the material is vibrated, crushed, and impacted.

• Compactive effort: static weight and vibration.


65


Vibrating drum on smooth-wheel roller

• Vertical vibrator attached to smooth wheel rollers.

• The best explanation of why roller vibration causes densification of granular soils is that particle rearrangement occurs due to cyclic deformation of the soil produced by the oscillations of the roller.

• Compactive effort: static weight and vibration.

• Suitable for granular soils


66

5.1 Equipment-Summary


67

5.2 Variables-Vibratory Compaction

•There are many variables which control the vibratory compaction or densification of soils.•Characteristics of the compactor:•(1) Mass, size•(2) Operating frequency and frequency range

•Characteristics of the soil:•(1) Initial density•(2) Grain size and shape•(3) Water content

•Construction procedures:•(1) Number of passes of the roller•(2) Lift thickness•(3) Frequency of operation vibrator•(4) Towing speed


68

5.3 Dynamic Compaction

Dynamic compaction was first used in Germany in the mid-1930’s.

The depth of influence D, in meters, of soil undergoing compaction is conservatively given by

D ≈ ½ (Wh)1/2

W = mass of falling weight in metric tons.

h = drop height in meters

From Holtz and Kovacs, 1981

69

5.4 Vibroflotation

From Das, 1998

Vibroflotation is a technique for in situ densification of thick layers of loose granular soil deposits. It was developed in Germany in the 1930s.

70

5.4 Vibroflotation-Procedures

Stage1: The jet at the bottom of the Vibroflot is turned on and lowered into the ground

Stage2: The water jet creates a quick condition in the soil. It allows the vibrating unit to sink into the ground

Stage 3: Granular material is poured from the top of the hole. The water from the lower jet is transferred to he jet at the top of the vibrating unit. This water carries the granular material down the hole

Stage 4: The vibrating unit is gradually raised in about 0.3-m lifts and held vibrating for about 30 seconds at each lift. This process compacts the soil to the desired unit weight.

From Das, 1998

71

6. Field Compaction Control and Specifications

72

6.1 Control Parameters

• Dry density and water content correlate well with the engineering properties, and thus they are convenient construction control parameters.

• Since the objective of compaction is to stabilize soils and improve their engineering behavior, it is important to keep in mind the desired engineering properties of the fill, not just its dry density and water content. This point is often lost in the earthwork construction control.


73

6.2 Design-Construct Procedures

• Laboratory tests are conducted on samples of the proposed borrow materials to define the properties required for design.

• After the earth structure is designed, the compaction specifications are written. Field compaction control tests are specified, and the results of these become the standard for controlling the project.


74

6.3 Specifications

(1) End-product specifications•This specification is used for most highways and building foundation, as long as the contractor is able to obtain the specified relative compaction , how he obtains it doesn’t matter, nor does the equipment he uses.•Care the results only !•(2) Method specifications•The type and weight of roller, the number of passes of that roller, as well as the lift thickness are specified. A maximum allowable size of material may also be specified.•It is typically used for large compaction project.


75

6.6.1 Destructive Methods


Methods(a) Sand cone

(b) Balloon

(c) Oil (or water) method

Calculations•Know Ms and Vt

•Get ρd field and w (water content)

•Compare ρd field with ρd max-lab and calculate relative compaction R.C.

(a)

(b)

(c)

76

6.6.1 Destructive Methods (Cont.)

•Sometimes, the laboratory maximum density may not be known exactly. It is not uncommon, especially in highway construction, for a series of laboratory compaction tests to be conducted on “representative” samples of the borrow materials for the highway. If the soils at the site are highly varied, there will be no laboratory results to be compared with. It is time consuming and expensive to conduct a new compaction curve. The alternative is to implement a field check point, or 1 point Proctor test.


77

6.6.1 Destructive Methods (Cont.)• The measuring error is mainly from the determination of

the volume of the excavated material.

• For example,• For the sand cone method, the vibration from nearby working

equipment will increase the density of the sand in the hole, which will gives a larger hole volume and a lower field density.

• If the compacted fill is gravel or contains large gravel particles. Any kind of unevenness in the walls of the hole causes a significant error in the balloon method.

• If the soil is coarse sand or gravel, none of the liquid methods works well, unless the hole is very large and a polyethylene sheet is used to contain the water or oil.

tsfieldd V/M=ρ −


78

6.6.2 Nondestructive Methods


Nuclear density meter(a) Direct transmission

(b) Backscatter

(c) Air gap

(a)

(b)

(c)

PrinciplesDensityThe Gamma radiation is scattered by the soil particles and the amount of scatter is proportional to the total density of the material. The Gamma radiation is typically provided by the radium or a radioactive isotope of cesium.

Water contentThe water content can be determined based on the neutron scatter by hydrogen atoms. Typical neutron sources are americium-beryllium isotopes.

79

6.6.2 Nondestructive Methods (Cont.)

•Calibration•Calibration against compacted materials of known density is necessary, and for instruments operating on the surface the presence of an uncontrolled air gap can significantly affect the measurements.

80

7. Estimating Performance of Compacted Soils

81

7.1 Definition of Pavement Systems


STORAGE TANKS

82AR-414 Earthquake Resistant Building Design Earthquake Resistant Construction Details


In general there are three kinds of water tanks-1.Tanks resting on ground, 2.Underground tanks and3.Elevated tanks.


From design point of view the tanks may be classified as per their shape-

RECTANGULAR TANKSCIRCULAR TANKSINTZE TYPE TANKSSPHERICAL TANKSCONICAL BOTTOM TANKSSUSPENDED BOTTOM TANKS.


The tanks resting on ground like clear water reservoirs, settling tanks, aeration tanks etc. are supported on the ground directly.• The walls of these tanks are subjected to pressure and the base is subjected to weight of water and pressure of soil.•The tanks may be covered on top.


The tanks like purification tanks, Imhoff tanks, septic tanks, and gas holders are built

UNDERGROUND. 1. The walls of these tanks are subjected to water pressure from inside and the earth pressure from outside. 2. The base is subjected to weight of water and soil pressure. These tanks may be covered at the top.


ELEVATED TANKS are supported on staging which may consist of masonry walls, R.C.C. tower or R.C.C. columns braced together. The walls are subjected to water pressure.

The base has to carry the load of water and tank load.The staging has to carry load of water and tank.The staging is also designed for wind forces.


1. Ground Supported Rectangular Concrete Tank


2. Elevated Tank Supported on 4 Column RC Staging


3. Elevated Intze Tank Supported on 6 Column RC Staging


DESIGN OF RCC OVERHEAD WATER TANKS -

TERMINOLOGY -

1. Capacity - Capacity of the tank shall be the volume of water it canstore between the designed full supply level and lowest supply level ( thatis, the level of the lip of the outlet pipe ). Due allowance shall be madefor plastering the tank from inside if any when calculating the capacity oftank.

2. Height of Staging - Height of staging is the difference between thelowest supply level of tank and the average ground level at the tank site.

3. Water Depth - Water depth in tank shall be difference of level betweenlowest supply level and full supply level of the tank.


LAYOUT OF OVERHEAD TANKS

Generally the shape and size of elevated concrete tanks for economical design depends upon the functional requirements such as:a) Maximum depth for water;b) Height of staging;c) Allowable bearing capacity of foundation strata and type of foundation suitable;d) Capacity of tank; ande) Other site conditions.


Classification and Layout of Elevated Tanks -

1. For tank up to 50 m3 capacity may be square or circular in shape

and supported on staging three or four columns.

2. Tanks of capacity above 50 m3 and up to 200 m3 may be square or circular in plan and supported on minimum four columns.

3. For capacity above 200 m3 and up to 800 m3 the tank may be square, rectangular, circular or intze type tank. The number of columns to be adopted shall be decided based on the column spacing which normally lies between 3.6 and 4.5 m. For circular, intze or conical tanks, a shaft supporting structures may be provided.

94

Staging Components

COLUMNS





Bracings

For staging of height above foundation greater than 6 m, the column shall be rigidly connected by horizontal bracings suitably spaced vertically at distances not exceeding 6 m.






DETAILING -



Bibliography -

• Emmitt, S. and Gorse, C. (2010) Barry’s Introduction to Construction of Buildings. Oxford, Blackwell Publishing

• Emmitt, S. and Gorse, C. (2010) Barry’s Advanced Construction of Buildings. Oxford, Blackwell Publishing

• IS: 11682-1985 (CRITERIA FOR DESIGN OF RCC STAGING FOR OVERHEAD WATER TANKS).

• IITK-GSDMA GUIDELINES for SEISMIC DESIGN OF LIQUID STORAGE TANKS.

• Google Images.

107

Thanks to one and all…..

Presented to,Ar. Anju soni mamon,9th October 2014

AR-414 Earthquake Resistant Building Design Earthquake Resistant Construction Details

Earthquake Resistant Design Techniques

Engineering

buildings earthquake

earthquake prone

earthquake engineering

stone masonry foundation

foundation bed concrete

thickness of foundation

lowrise buildings

urban buildings