Design and Analysis of Seismic Forces in Multi-Storey Building … · 2017. 2. 25. · Design and Analysis of Seismic Forces in Multi-Storey Building with Water Tank as Liquid Damper

International Journal of Trend in Research and Development, Volume 4(1), ISSN: 2394-9333

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IJTRD | Jan-Feb 2017 Available [email protected] 586

Design and Analysis of Seismic Forces in Multi-Storey

Building with Water Tank as Liquid Damper N Shruthi Das

Assistant Professor, Guru Nanak Institute of Technical Campus, Hyderabad, Telangana State, India

Abstract: The principle objective of this project is to analyse and

design a multi-storeyed building G+10 (3 dimensional frame)

using ETABS 2015. The design involves load calculations

manually and analyzing the whole structure by ETABS 2015. The

design methods used in ETABS 2015 analysis are Limit State

Design conforming to Indian Standard Code of Practice. ETABS

features a state-of-the-art user interface, visualization tools,

powerful analysis and design engines with advanced finite

element and dynamic analysis capabilities. From model

generation, analysis and design to visualization and result

verification, ETABS 2015 is the professional‟s choice. Initially

we started with the analysis of simple 2 dimensional frames and

manually checked the accuracy of the software with our results.

The results proved to be very accurate. We analyzed and designed

a G + 10 storey building [2-D Frame] initially for all possible

load combinations [Dead, Live, Wind and Seismic Loads].

Several technologies are available to minimize the

vibration of structures, of which, use of Tuned Liquid Damper

(TLD) is a recent development. TLD is traditionally made of rigid

tank filled with water. Once excited, the water inside the tank

experiences sloshing motion as a result of building vibration and

dissipates energy through the sloshing and wave-breaking of the

liquid.

This project aims to study the effectiveness of TLD in

reducing seismic vibration of a two-storied building frame when

it is subjected to horizontal excitations.

Analytical study of the undamped frame was carried out

in ANSYS WORK BENCH software. Based on modes and

frequencies obtained from analytical study, dimensions of steel

building frame were fixed and experimental study was carried out

by shake table experiments. Also various parameters that

influence the effectiveness of TLD are studied.

Keywords: Dampers, Horizontal excitation, Sloshing, Tuned

Liquid Damper, Vibration Control

I. INTRODUCTION

Importance of Seismic Design Codes Ground vibrations

during earthquakes causes forces and deformations in structures.

Structures need to be designed to withstand such forces and

deformations. Seismic codes help to improve the behaviour of

structures so that they may withstand the earthquake effects

without significant loss of life and property. Countries around the

world have procedures outlined in seismic codes to help design

engineers in the planning, designing, detailing and constructing of

structures. An earthquake-resistant building has four virtues in it,

namely: (a) Good Structural Configuration: Its size, shape and

structural system carrying loads are such that they ensure a direct

and smooth flow of inertia forces to the ground. (b) Lateral

Strength: The maximum lateral (horizontal) force that it can resist

is such that the damage induced in it does not result in collapse.

(c) Adequate Stiffness: Its lateral load resisting system is such

that the earthquake-induced deformations in it do not damage its

contents under low-to moderate shaking. (d) Good Ductility: Its

capacity to undergo large deformations under severe earthquake

shaking even after yielding is improved by favorable design and

detailing strategies. Seismic codes cover all these aspects. Indian

Seismic Codes Seismic codes are unique to a particular region or

country.

A. Component Parts Of Building

A building is defined as any structure constructed for human

habitation and any other purpose. It has three major components,

namely:

Foundation

Plinth

Superstructure

Foundation

It is the lowest artificially prepared part, below the surface of the

ground which is in direct contact with substrata and transmits the

load to the subsoil

Plinth

It is the middle part of the structure, above the surface of the

ground and up to the surface of the floor

Superstructure

The part of the structure above the plinth level is called

superstructure.

II. LITERATURE REVIEW

A. General

Among the various seismic response control devices, TMD

proved to be successful in reducing the seismic response. Passive

TMD can be structure, connected to the main structure by means

of springs and the parameter of TMD is tuned to that of main

structure such that the dynamic response of main structure during

Earthquake is reduced. Instead of connecting a separate part to

the main structure, usage of water tank as passive TMD which is

an integral part of structure is advantageous. Work on usage of

water tank as passive TMD is being carried out and some papers

are presented in which results prove to reduce seismic response.

B. Critical Appraisal of Literature

Sadek et al. (1997) [1], the optimum parameters of Tuned Mass

Damper (TMD) that result in considerable reduction in the

response of structures to seismic loading are presented. The

criterion used to obtain parameters is to select, for a given mass

ratio, the frequency (tuning) and damping ratios that would result

in equal and large modal damping in the first two modes of

vibration. The parameters are used to compute the response of

several single and multi-degree of freedom structures with TMDs


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to different earthquake excitations. The results indicate that the

use of the proposed parameters reduces the displacement and

acceleration significantly. The method can also be used in

vibration control of tall buildings using the so called „mega sub–

structure configuration‟, where substructures serve as vibration

absorbers for the main structure. It is shown that by selecting the

optimum TMD parameters as proposed in this paper, significant

reduction in the response of tall buildings can be achieved. It was

found that the equal damping ratios in the first two modes are

greater than the average of damping ratios of lightly damped

structure and heavily damped TMD.

Properly designed tuned-mass control systems can be

characterized as follows:

They reduce seismically induced responses in terms of

displacements, accelerations, internal stresses and strains as

well as subsoil demands.

They increase the structural safety. The collapse of a

building becomes less probable and hence, human life is

protected.

They improve the serviceability of structures. Damage and

corresponding repair cost in case of seismic events are

reduced significantly.

In comparison to conventional strengthening methods, the

building can usually be under operation during the

installation of the TMCS (if no additional measures are

required).

Regarding the overall procedure and required material for

the installation of a tuned mass system this strategy can be

classified as 'cost effective„

III. DAMPERS IN STRUCTURES AND TIME HISTORY

ANALYSIS

A. General

Earthquake is one of the major catastrophic events for destroying

cities and its inhabitants. During the last few decades researchers

from around the globe put extensive efforts to achieve sustainable

solution to diminish the direct effects caused by earthquakes,

which have led to the innovation of various control devices.

A large amount of energy is imparted into a structure

during earthquake ground motions. Conventional design

philosophy seeks to prevent collapse by allowing structural

members to absorb and dissipate the transmitted earthquake

energy by inelastic cyclic deformations in specially detailed

regions.

B. Dampers

Damping is one of many different methods that have been

proposed for allowing a structure to achieve optimal performance

when it is subjected to seismic, wind storm, blast or other types of

transient shock and vibration disturbances. Conventional

approach would dictate that the structure must inherently

attenuate or dissipate the effects of transient inputs through a

combination of strength, flexibility and deformability. The level

of damping in a conventional elastic structure is very low. During

strong motions such as earthquakes conventional structures

usually deform well beyond their elastic limits and eventually fail

or collapse. Therefore, most of the energy dissipated is absorbed

by the structure itself through localized damage as it fails.

1. Tuned Systems

Tuned systems are supplemental devices attached to structures to

reduce vibrations due to wind, earthquakes or other dynamic

loading conditions. Because the natural frequencies of these

devices are equal or close to those of the structures to which they

are attached, they are called tuned systems. This category of

passive devices includes tuned mass dampers and tuned liquid

dampers. Tuned devices are relatively easy to implement in new

buildings and in the retrofit of existing ones. They do not require

any external power source to operate and do not interfere in

horizontal and vertical load paths.

1.1 Tuned Mass Dampers

A tuned mass damper, also known as a harmonic absorber, is a

device mounted in structures to reduce the amplitude of

mechanical vibrations. Their application can prevent discomfort,

damage, or outright structural failure. They are frequently used in

power transmission, automobiles, and buildings. Then, the excess

energy that is built up in the structure can be transferred to a

secondary mass and is dissipated by the dashpot due to relative

motion between them at a later time. Mass of the secondary

system varies from 1-10% of the structural mass. As a particular

earthquake contains a large number of frequency content now a

days multiple tuned mass dampers (MTMD) has been used to

control earthquake induced motion of high rise structure. Often

for better response control multiple-damper configurations

(MDCs) which consist of several dampers placed in parallel with

distributed natural frequencies around the control tuning

frequency is used. For the same total mass, a multiple mass

damper can significantly increase the equivalent damping

introduced to the system.

Fig.3.1 Tuned mass damper

1.2 Tuned Liquid Dampers

Tuned liquid dampers which have been extensively used in

marine vessels and space satellites are being implemented in

structure for earthquake vibration control. Tuned liquid dampers

consists of rigid tanks filled with shallow fluid where the sloshing

motion absorbs the energy and dissipates through viscous action

of the fluid, wave breaking and auxiliary damping appurtenances

such as nets or floating beads. The principle of absorbing the

kinetic energy of the structure is similar to TMD's where the fluid

functions as moving mass and the restoring force is generated by

gravity. TLD's have several advantages over TMD's such as

reducing the motion in two directions simultaneously and not

requiring large stroke lengths. On the other hand, the relatively

small mass of water or other fluids compared to the large mass of

TMD's necessitates larger spaces to achieve greater damping

effect. TLD's are effective in reducing the response of structures

subjected to harmonic and wind excitations. An example of the


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application of TLD's is the 149.4m high Shin Yokohama Prince

Hotel in Japan with 30 TLD units attached to the top floor to

suppress wind induced vibrations.

Fig.3.2 Tuned liquid damper

C. Metallic Dampers

One of the effective mechanisms available for the dissipation of

energy input to a structure from an earthquake is through inelastic

deformation of metals. The idea of utilizing added metallic

energy dissipaters within a structure to absorb a large portion of

seismic energy began with the conceptual and experimental work

by Kelly etal. and skinner etal. Several of the devices considered

include torsion beams, flexural beams and U-strip energy

dissipaters. During ensuing years, a wide variety of such devices

have been studied. Many of the devices use mild steel plates with

triangular or X - shapes so that yielding is almost spread

throughout the material.

This type of energy dissipation devices utilizes the

hysteretic behavior of metals in the inelastic range. The resisting

force of the dampers therefore depends on the non -linear stress

strain characteristics of the material. Different devices that utilize

flexure, shear or extensional deformation in the plastic range have

been developed. The advantages of this type of dampers are their

stable behavior, long term reliability and good resistance to

environmental and thermal conditions. Moreover metallic

dampers are capable of providing buildings with increased

stiffness, strength and energy dissipation capacity. Metal yielding

devices are widely used due to their simplicity in both design and

implementation and the devices dissipate energy by taking

advantage of the material‟s stable hysteretic behavior.

Generally there are three major types of metallic dampers.

BRB dampers

ADAS dampers

TADAS dampers

1. B.R.B. Dampers

A BRB damper consists of a steel brace (usually having low-yield

strength) with a cruciform cross section that is surrounded by a

stiff steel tube. The region between the tube and brace is filled

with a concrete-like material and a special coating is applied to

the brace to prevent it from bonding to the concrete. Thus, the

brace can slide with respect to the concrete-filled tube.

In many cases, BRB dampers are installed within a

chevron bracing arrangement. In this case, under lateral load, one

damper is in compression and the other is in tension, and hence

zero vertical loads are applied at the intersection point between

the dampers and the beam above. In this regard, the dampers may

be regarded as superior to a conventional chevron bracing

arrangement where the compression member is expected to

buckle elastically, leaving a potentially large unbalanced vertical

force component in the tension member that is, in turn, applied to

the beam above.

2. ADAS Dampers

This device consists of a series of steel plates wherein the bottom

of the plates are attached to the top of a chevron bracing

arrangement and the top of the plates are attached to the floor

level above the bracing .As the floor level above deforms laterally

with respect to the chevron bracing, the steel plates are subjected

to a shear force. The shear forces induce bending moments over

the height of the plates, with bending occurring about the weak

axis of the plate cross section. The geometrical configuration of

the plates is such that the bending moments produce a uniform

flexural stress distribution over the height of the plates. Thus,

inelastic action occurs uniformly over the full height of the plates.

For example, in the case where the plates are fixed-

pinned, the geometry is triangular. In the case where the plates

are fixed, the geometry is an hourglass shape. To ensure that the

relative deformation of the ADAS device is approximately equal

to that of the storey in which it is installed, the chevron bracing

must be very stiff.

Fig 3.6 Metallic X-plate damper

The hysteretic behavior of an ADAS damper is

similar to that of a BRB damper and can be represented by

various mathematical models that describe yielding behavior of

metals. As for the BRB dampers, the dissipated energy in an

ADAS damper is the result of inelastic material behavior and thus

the ADAS damper will be damaged after an earthquake and may

need to be replaced.

D. Shear Yielding Dampers

Shear panels represent an interesting solution to resist

lateral forces and to control the dynamic response of framed

buildings. Due to their considerable shear stiffness and strength,

they can be favorably used as a seismic resistance system under


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both moderate and strong earthquake loading. In addition, when

designed as dissipative elements, shear panels can be viably used

for the seismic protection of the primary structure, due to the

large energy dissipation capacity related to the large portion

where plastic deformations take place. As far as the stiffening

effect is concerned, it has been already recognized that even

lightweight metal shear panels may considerably improve the

structural performance of the structure at the serviceability limit

state.

E. Time History Analysis

1. General

Time history analysis is a step by step procedure of the dynamic

response of the structure to a specified loading that may vary with

time. The analysis may be linear or nonlinear. Time history

analysis is used to determine the dynamic response to a structure

subjected to arbitrary loading. The dynamic equilibrium

equations to be solved are given by

𝐌𝐱 + 𝐂𝐱 +𝐊𝐱 = 𝐫(𝐭)

2. Initial Conditions

The initial conditions that describe the state of structure at the

beginning of time history case.

These include

• Displacements and velocities

• Internal forces and stresses

• Internal state variables for non -linear elements

• Energy values for the structure

• External loads

The accelerations are not considered initial conditions, but are

computed from the equilibrium equation. For linear transient

analyses, zero initial conditions are always assumed. For periodic

analyses, the program automatically adjusts the initial conditions

at the start of the analysis to be equal to the conditions at the end

of the analysis.

3. Time Steps

Time history analysis is performed at discrete time steps.

One may specify the number of output time steps with parameter

"nstep" and the size of the time steps with parameter "dt" The

time span over which the analysis is given by nstep. dt. Response

is also calculated, at every time step of the input time functions in

order to accurately capture the full effect of the loading. These

time steps are call load steps. For modal time-history analysis,

this has little effect on efficiency.

4. Modal Time History Analysis

Modal superposition provides a highly efficient and

accurate procedure for performing time-history analysis. Closed-

form integration of the modal equations is used to compute the

response, assuming linear variation of the time functions, f i (t),

between the input data time points. Therefore, numerical

instability problems are never encountered, and the time

increment may be any sampling value that is deemed fine enough

to capture the maximum response values.

IV. RESULTS & DISCUSSIONS

In this chapter, modeling of liquid sloshing in TLDs is

presented. The first approach is aimed at understanding the

underlying physics of the problem based on a “Sloshing-

Slamming (S2)” analogy which describes the behavior of the

TLD as a linear sloshing model augmented with an impact

subsystem. The second model utilizes certain nonlinear functions

known as impact characteristic functions, which clearly describe

the nonlinear behavior of TLDs in the form of a mechanical

model. The models are supported by numerical simulations which

highlight the nonlinear characteristics of TLDs.

A. Introduction

The motion of liquids in rigid containers has been the

subject of many studies in the past few decades because of its

frequent application in several engineering disciplines. The need

for accurate evaluation of the sloshing loads is required for

aerospace vehicles where violent motions of the liquid fuel in the

tanks can affect the structure adversely

1. Mechanical Modeling of TLDs

For convenient implementation in design practice, a

better model for liquid sloshing would be to represent it using a

mechanical model. This is helpful in combining a TLD system

with a given structural system and analyzing the overall system

dynamics. Some of the earliest works in this regard are presented

in Abramson (1966). Most of these are linear models based on the

potential formulation of the velocity field. For shallow water

TLDs, various mechanisms associated with the free liquid surface

come into play to cause energy dissipation. These include

hydraulic jumps, bores, breaking waves, turbulence and impact

on the walls (Lou et al. 1980). The linear models fail to address

the effects of such phenomena on the behavior of the TLD.

Sloshing-Slamming (S2) Damper Analogy

The sloshing-slamming (S2) analogy is a combination of two

types of models: the linear sloshing model and the impact damper

model.

Modeling of Tuned Liquid Column Dampers

Figure 3.1 shows the schematic of the TLCD mounted on a

structure represented as a SDOF system.

Figure 4.1 Schematic of the Structure-TLCD system

B. Building Specification

An existing OGS framed building located at Guwahati,

India (Seismic Zone V) is selected for the present study. The

building is fairly symmetric in plan and in elevation.

No. of Floors of Building – G+10

Slab Thickness – 150 m

Each Floor Height – 3 m


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Total Height of the Building – 36 m

External Wall Thick – 230 mm

Internal Thickness – 120 mm

For Live Load – 3 kN/m

Column Sizes – 400 x 450 mm

Beam Sizes – 300 x 450 mm

The cross sections of the structural members (columns 400

mm×450 mm and beams 300 x 450 mm) are equal in all frames

and all stories. Storey masses to 295 and 237 tonnes in the bottom

storyes and at the roof level, respectively. The design base shear

was equal to 0.15 times the total weight.

Figure 4.2.Maximum Storey Displacement of G+10 Building

C. For Calculation of Dead Load

Self- weight- 1 kn/Sq.m

Floor load -2 kN/Sq.m

External wall Thickness – 230mm

For Density of Brick Wall = 20 kN/ m2

= 20 x 0.23 x 3

= 13.8 kN/m3

Internal wall Thickness – 120mm

For Density of Brick Wall = 20 kN/ m2

= 20 x 0.12 x 3

= 7.2 kN/m3

For Considering of Floor Load -1.8 kN/m2

Live Load – 3kN/ m

Figure 4.3: Dead Load on G+10 Building

Figure 4:.Self -Weight of G+10 Building

Figure 5.Max Storey displacement G+10 Building

C. Analysis Results

This chapter provides analysis results. Storey Response -

Maximum Storey Displacement

Summary Description

This is storey response output for a specified range of stories and

a selected load case or load combination. This is storey response

output for a specified range of stories and a selected load case or

load combination.

Figure 7: Shear Force on G+10 Building

Seismic Weight of Floors

The seismic weight of each floor is its full dead load plus

appropriate amount of imposed load, as specified in 7.3.1 and

7.3.2. While computing the seismic weight of each floor, the

weight of columns and walls in any storey shall be equally

distributed to the floors above and below the storey.


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Table 1: Storey Response Values

Storey Elevation Location X-Dir Y-Dir

m

Storey12 34.5 Top 2.828E-08 5.113E-09

Storey11 33 Top 9.151E-08 6.768E-09

Storey10 30 Top 1.445E-07 7.533E-09

Storey9 27 Top 1.962E-07 8.026E-09

Storey8 24 Top 2.448E-07 8.436E-09

Storey7 21 Top 2.895E-07 8.683E-09

Storey6 18 Top 3.294E-07 8.712E-09

Storey5 15 Top 3.634E-07 8.453E-09

Storey4 12 Top 3.905E-07 7.82E-09

Storey3 9 Top 4.074E-07 6.697E-09

Storey2 6 Top 3.991E-07 0

Storey1 3 Top 2.568E-07 0

Base 0 Top 0 0

Seismic Weight of Building

The seismic weight of the whole building is the sum of the

seismic weights of all the floors. Any weight supported in

between storeys shall be distributed to the floors above and below

in inverse proportion to its distance from the floors.

Figure 7:.Displacement of Seismic Load on G+10 Building

Figure 8: Earthquake Load on G+10 Building

D. Design Of Water Tank

Introduction: A water tank is used to store water to tide over the

daily requirements.

In general water tank can be classified under three heads:

Tanks resting on ground.

Elevated tanks supported on staging.

Underground water tanks.

From the shape point of view, water tanks may be several types,

such as

Circular water tanks.

Rectangular water tanks.

Spherical water tanks.

Intzetank.

Circular tank with conical bottom.

Design of rectangular tank

Number of flats= 4x4 = 16

Number of members in a family = 6

Water demand per capita=135lits/day

Water requirement = 16x6x135 = 12960 lits

Reserve = 12960 lits

Total Water Storage= 25920 ( Say 30,000 lits)

Therefore, V = 30 m3

Height of the water tank H= 1.75m

Freeboard = 0.15m

Therefore, height of water = 1.6m

Area of tank required = 30/1.6 = 18.75 m2

Assume thickness of wall = 100 mm

Provide 2 tanks: (3.75x2.5x1.6)

a= 1.6m b=3.75m c=2.5m

b/a= 2.5 c/a= 2

B.M. COEFFICIENTS

LONG WALL &SHORT WALL

Mx My

Mx Mz

+αx= +0.012 + αy = +0.027

+αx = +0.015 + αz= +0.027

- αx= -0.013 - αy = -0.074

- αx = -0.100 - αz = -0.06

BM =αγa3 (γ=10 a=1.6)

B.M.

+ Mx = +0.643 + My = +1.5

+ Mx = +0.80 +Mz= +1.5

- Mx = -0.7 -My = -4

- Mx = -5.36 - Mz= -3.21

Design of Short Wall (x-y)

Vertical Reinforcement

Outer Face: M= 5.36 KN-m but Mmin=9.38 KN-m

Provide 10mm φ @ 200mm c/c

Inner Face: M= 0.8x106 N-mm


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Horizontal Reinforcement

Outer Face: M= 1.5 KN-m


Inner Face: M= 4x106 N-mm =>Ast= 457.48 mm2

Provide 10mm φ @ 200mm c/c(y-z)

Inner Face: M= 4 KN-m Provide 10mm φ @ 200mm c/c

Outer Face: M= 1.5 KN-m Provide 10mm φ @ 200mm c/c

CONCLUSIONS

The tasks of providing full seismic safety for the

residents inhabiting the most earth quake prone regions are far

from being solved. However in present time we have new

regulations in place for construction that greatly contribute to

earthquake disaster mitigation and are being in applied in

accordance with world practice.

In the regulations adopted for implementation in India the

following factors have been found to be critically important in the

design and construction of seismic resistant buildings:

• Sites selection for construction that are the most favorable

in terms of the frequency of occurrence and the likely

severity of ground shaking and ground failure;

• High quality of construction to be provided conforming to

related IS codes such as IS 1893 , IS 13920 to ensure good

performance during future earthquakes.

• To implement the design of building elements and joints

between them in accordance with analysis .i.e. ductility

design should be done.

• Structural-spatial solutions should be applied that provide

symmetry and regularity in the distribution of mass and

stiffness in plan and in elevation.

Finally it is concluded that control systems are classified

as passive control, active control, semi active control, and a

combination of passive and active or semi-active control.

COPE FOR THE FURTHER INVESTIGATION

Studying the seismic behavior of structures by placing

water tanks at various positions.

Studying the seismic behavior of unsymmetrical building,

placing water tank at a position such that seismic response

is reduced.

Studying the seismic behavior of structures with and

without water tank subjected to different types of

Earthquake data.

SUMMARY

In this project, the conclusions drawn from the present study are

given. Also the scope for further investigation based on the

present study was discussed.

References

[1] Fahim Sadek, BijanMohraz, Andrew W. taylor and Riley

M.Chung (1997), “A method of estimating the parameters

of tuned mass dampers for seismic applications”,

Earthquake Engineering and Structural Dynamics,

26:617-635.

[2] Dorothy Reed, Jinkyu Yu, Harry Yeh,

SigurdurGardarsson (1998), “Investigation of tuned liquid

dampers under large amplitude excitation”, ASCE,

Journal of Engineering Mechanics, 124:405-413.

[3] Bruno Palazzo, Luigi Petti (1999), “Combined control

strategy: Base isolation and Tuned mass damping”, ISET,

Journal of earthquake engineering, 36:121-137.

[4] Peter Nawrotzki (Oct 2006), “Tuned-Mass Systems for

the seismic retrofit of buildings”, Seventh International

Congress on Advances in Civil Engineering, Yildiz

Technical University, Istanbul, Turkey.

Documents

Design and Analysis of Seismic Forces in Multi-Storey Building … · 2017. 2. 25. · Design and Analysis of Seismic Forces in Multi-Storey Building with Water Tank as Liquid Damper