507 33 Powerpoint-slides DRCS Ch20

8/12/2019 507 33 Powerpoint-slides DRCS Ch20

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Oxford University Press 2013. All rights reserved.

Design of Reinforced

Concrete Structures

N. Subramanian


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Chapter 20

Design of Multi-storey

Buildings


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Introduction

Most of the buildings in Indian cities have ground plus three floors.

The recent trend is to construct buildings with at least 1015 storeys, so

that the massive housing and commercial needs are satisfied (see Fig.

20.1).

Most of these buildings are made of reinforced concrete (RC). Mass of

concrete floor slabs, beams, and columns of RC construction is higher

than that of comparable steel construction.


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Heading

Fig. 20.1 Construction of a multi-storey building in Chennai


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Introduction

This results in larger earthquake-induced bending moments and axial

forces. As the height of a building increases, the behaviour of the

structure becomes more complex.

Such buildings are more sensitive to wind and earthquake loads and

hence, need to be very carefully designed and detailed.

Wind influences the design of structural system of tall buildings as

well as their shape and form.


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Since daylighting design has a large impact on the sustainability of the

design, the faade may be one of the most important factors in

controlling the daylight and shadow that enters a high-rise structure.

The latest trend is the use of double skin, and occasionally triple skin,

faade with ventilation systems. Double glazing with argon-filled

cavities, triple-glazing, and glass coating can increase U-values.

Introduction


7/21 Oxford University Press 2013. All rights reserved.

With careful design, high-rise structures can be aerodynamically

designed to resist high wind speeds and to simultaneously utilize them,by using strategically placed wind turbines, thus producing more energy

with no risk to the safety of the buildings users.

Multi-storey buildings are often analysed, designed, and detailed

using commercially available software.

The commercial software packages available in the market include

STAAD.Pro, SAP 2000, ETABS, SAFE, Nastran, Midas NFX, ANSYS, and

STRUDS. Many of these programs have analysis and design capabilities.

Introduction



Special structural design packages are also available and some

engineers have developed their own spreadsheets for the design of

structural elements (e.g., FRAME, RC Slab, RC Beam, and RC Foundation

developed by Computer Design Consultants).

AutoCAD is the most preferred detailing tool.

Linear analysis is considered sufficient for buildings having 15 storeys,

whereas dynamic analysis is preferred for regular buildings in high

seismic zones and having height greater than 40 m, irregular buildings,

and slender buildings subjected to heavy wind loads.

Introduction



Estimation of Loads

STAAD.Pro is capable of estimating self-weight of the frame elements

modelled.

The user needs to provide the input for the loadings, which needs to

be considered for the analysis.

The different loadings, which need to be defined for the analysis of

buildings are given as follows:

1. Dead Load

2. Live Load

3. Earthquake Load



Analysis of Structure

A structure needs to be analysed for gravity and earthquake/ wind

loads.

Gravity loads are those that are more or less constant over the lifetime

of a structure.

The static analysis for gravity loads is much simpler compared to the

dynamic analysis for the earthquake/wind loads.



1. Gravity Load Analysis: The space frame is modelled using software

STAAD.Pro.

2. Lateral Load Analysis: Two different seismic analyses, namely

equivalent static and response spectrum, are considered for this

purpose. Both the analyses are carried out using the STAAD.Pro

software.

Analysis of Structure

R i f d C D i U i



Reinforced Concrete Design Using

STAAD.Pro For Indian Codes

STAAD. Pro has the capacity to design the frame elements through its

in-built subroutines.

It has different country codes in its library; hence, the given frame can

be designed for the Indian, American, British codes, etc.

The user needs to provide different parameters as mentioned in page

796 of the book to obtain correct results using STAAD.Pro.



Design Parameters as per IS 13920Following design parameters in addition to IS456 parameters need to

be used

1. Design Parameter Gravity Load Design:

Shear force to be resisted by the vertical hoops shall be the

maximum of the following:

1. Calculated factored shear force as per analysis

2. Shear force due to formation of plastic hinges at both

ends of the beam plus the factored gravity load on the

span

In STAAD.Pro, we need to specify gravity load case number to

generate UDL on beam. Gravity load case can be generated by using

repeat load or unfactored load combination.



2. Design Parameter PLASTIC: To calculate the plastic hogging and

sagging moments of resistance at beam ends, the parameter is

entered as one. If this parameter is not given (default value = 0),

then STAAD.Pro calculates the plastic hogging and sagging moments

of resistance.

3. Design Parameter IPLM: This parameter is specified if it is not

necessary to calculate the plastic or elastic hogging and sagging

moments of resistance at either the start or end of the beam. Thismeans support may or may not be there at the beam start or end.

4. Design Parameter COMBINE

Design Parameters as per IS 13920



Strength Design of Columns

Columns are designed in STAAD.Pro through its in-built program.

IS 13920 is used for the design and the results are presented in this

section.



Strength Design of Columns

Fig. 20.2 Typical reinforcement detail for column marked C101


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Strength Design of Beams

Beams are designed in STAAD.Pro through its inbuilt program. IS

13920 is used for the design. Typical design details are shown in Page

799 of the book.

Reinforcement recommended by STAAD.Pro needs to be customized

to meet the practical conditions. Typical reinforcement details for beam

FB5 are shown in Fig. 20.3 (SP 34:1987).


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Design of Foundations

STAAD.Pro does not have an inbuilt facility for the design of

foundations.

There are separate specialized software for the design of foundations

(e.g., STAAD Foundation Advanced, Foundation 3D, Mat 3D, etc.).

The design parameters and design forces for the case study are given

in Page 801 of the book.


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Thank You!

507 33 Powerpoint-slides DRCS Ch20

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