design philosophy in structure design in civil engineering

S.N.P.I.T. & R.C.,UMRAKH

DESIGN PHILOSOPHY- Professor Urvesh N.Barot

- Assis. Professor Keyur P. Shah

1S.N.P.I.T. & R.C.

Presentation by:

Mehta Mrunali- 130490106064

Modi Nagma- 130490106065

Nakrani Akash- 130490106066

Nikam Sejal- 130490106067

Pansuriya Prashant- 130490106068

Patel Akshar- 130490106071

2S.N.P.I.T. & R.C.

DESIGN PHILOSOPHYThe main buildings in the stadium complex are

the stands, members and player's pavilion block,venue operating centre, media centre andlandscaped seating stand apart from servicebuildings and underground structures.

The structural system adopted for the buildingsare concrete/structural steel framed conventionalbeam slab and column structures on pile caps overbored cast-in-situ concrete piles/pre-cast concretepiles/green heart timber piles. The slabs areproposed in composite construction with concreteon profiled metal decking (serving asreinforcement). The stands are designed with pre-cast bleachers on raker beams in concrete/structuralsteel

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. The roof covering the stands are designed withstructural steel elements in profiled sections tomatch the architectural form. The columns in cast-in-situ concrete/structural steel have insertplates/base plates to seat the roof-supportingmember. The structures are analysed for deadload, live load and wind loads as per the codalprovisions. Waterproofing on concrete surfacesexposed to atmosphere is done with reinforcedmodified bituminous membrane and is protectedby cement concrete tiles. The waterproofing ofsunken slabs in toilets is also achieved with thesame material. All structural steel surfaces areprotected from corrosion with anti-corrosive paint.

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SERVICEABILITY:

It implies satisfactory performance of the structure under service loads, without discomfort to the user due ti excessive deflection, cracking, vibration and so on. Other considerations that comes under the preview of serviceability are durability, acoustic and thermal insulation etc.

The adverse effect of excessive deflections are:

1. it creates feeling of lack of safety

2. Asthetic view is spoiled.

3. Creates ponding of water on roof slabs

4. Cracking of floor finish materials

5. In machines, it result into misalignment of machines.

S.N.P.I.T. & R.C. 5

DESIGN LOADSDead LoadsThe self weight of the various elements are computed

based on the unit weight of materials as given below:

Material Unit Weight kN/m 3

Steel 78.5

Plain Cement Concrete 24

Reinforced Cement Concrete 25

Cement Concrete Screed 24

Soil 20

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Imposed Loads

As per BS:6399 (Part 1)-1996 the building is classifiedas Public Assembly building.

The superimposed loads or otherwise live load isassessed based on the occupancy classification asper BS:6399(Part 1)-1996 for assembly building. Theimposed loads (in kN/m2) considered are as listedbelow:

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Occupancy Classification Load (kN/m 2)

a) Assembly areas:

1) with fixed seats 4.0

2) without fixed seats 5.0

b) Kitchens, laundries 3.0

c) Stages 7.5

d) Corridors, hallways, stairs 4.0

e) Dressing rooms 2.0

f) Areas for equipment 2.0

g) Toilets and bathrooms 2.0

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On flat roofs, sloping roofs and curved roofs withslopes up to and including 10 degrees, the imposedloads due to use or occupancy of the buildings and thegeometry of the roofs are given below:

As per cl 6.2, BS:6399 (Part 1)-1996a) For roofs with access provision 1.5b) For roofs without access provision 0.75

On sloping roof of slope greater than 10o, as perclause 6.3 of BS:6399(Part1)-1996 the imposed loads(kN/m2 of the plan area) that are likely to actpermanently are as follows:

Waterproofing* 1.5 (On roof / terrace)

Partitions 1.0 (wherever applicable)

False ceiling 0.5 wherever applicable)9S.N.P.I.T. & R.C.

Structural slab shall be sloped suitably to avoidachieving requisite slopes with screed/brick bat coba

Bleachers are designed to resist a horizontal forceapplied to seats of 3.0 kN per linear meter along theline of seats and 1.5 kN per linear meter perpendicularto the line of seats.

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Wind Load

The wind pressure is calculated based on the datafurnished below and as per the provisions laid inBS:6399 (Part 2)-1997

Basic Wind speed = 50m/sec(As assessed from UBC)

Maximum gust = 30mph(13.5m/sec) As given

Mean probable = 50 years

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DESIGN LIFE OF STRUCTURE

Building Type factor Kb = 1.0

Ground roughness category = town

Built up areas with an average level of roof tops atleast Ho =5m above GL

Dynamic Augmentation Factor Cr

=0.03

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Static Simplified method is used for design forwind loads with the following parameters as per cl2.2 BS:6399 (Part2)-1997

Directional Factor Sd = 1.0Altitude Factor Sa = 1.0Seasonal Factor Ss = 1.0Probability Factor Sp = 1.0Site Wind Speed Vs = Vb x Sa x Sd x Ss x Sp

= 50 x 1 x 1 x 1 x 1 x 1 = 50m/secEffective Wind Speed = Vs x Sb

Where Sb is the terrain and building factorobtained from cl 2.2.3.3 of BS:6399(Part2)-1997

13S.N.P.I.T. & R.C.

Earthquake LoadGuyana is not within the earthquake belts and also

does not figure in the places listed in the

seismological active zones. It has been mentioned

that Guyana experiences tremors every 5-10 years.

Earthquake loads are not considered for analysis and

design. With the given conditions it is assumed that

the wind load on the structure would be sufficient

for the lateral loads that would be generated during

the tremors.

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Structural

Codes Description

Indian Standards

IS: 456-2000 Code of Practice for Plain and Reinforced Concrete

IS: 800-1984 Code of Practice for General Construction in Steel

IS: 808-1989 Dimensions for hot rolled steel beams, columns,

channels and angle sections

IS:875-1987(Part-1) Code of Practice for Design Loads (Other than

Earthquakes) for Buildings and Structures.

Dead Loads — Unit Weights of Building Materials

and Stored Materials



Imposed Loads



Wind Loads15S.N.P.I.T. & R.C.

Codes Description

Indian Standards



Special Loads and Load Combinations

IS:1786-1985 Specification for High Strength Deformed Steel

Bars and Wires for Concrete Reinforcement.

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Design process: analysis, design

and detailing: Analysis:

Structural analysis is necessary to determine thestress resultant like,

1. Shear stress

2. Bending moment

3. Axial force

4. Torsional moment

Acting at various cross sections of structuralelements. IS:456 permits the analysis of allstructures by linear elastic theory. Code alsopermit use of approximate methods likesubstitute frame method, use of coefficients forthe continuous beams and slabs.

For the analysis of statically determinatebeams and frames, conditions of staticequllibrium 17S.N.P.I.T. & R.C.

Structural analysis: modelling

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Design:

A systematically planned structure:

1. Should satisfy the functional requirements of the client and should be asthetic, which needs an architect.

2. Should be structurally safe so as to withstand the loads it has to bear, which needs a structure engineer.

The functional design of the building consists of planning the areas in best possible ways to obtain maximum usage and functions from the building. For a given residential bunglow,

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Functional planning

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The structural design is concerned with the strength of the building and its components. The aim of structural design is to decide the size of the member and provide appropriate reinforcements so that the structures being designed will perform satisfactorily during their intended life.

With the appropriate degree of safety, the structure should:

1. Sustain all loads

2. Sustain the deformation during and after construction

3. Should have adequate durability

4. Should have adequate resistance to misuse and fire

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Structural planning

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Detailing:

On completion of the structural design, the design ideas normally need to be communicated for construction at the site by translating them into detailed structural and comprehensive. In fact, an elaborate analysis becomes worthless if the computations are not translated effectively into the structural drawings.

Two main aims of RCC detailing are:

1. Providing an outline of the concrete to give necessary information regarding formwork to provide finished section of the desired size.

2. Providing enough reinforcement details for fabrication of the steel skeleton and its placement in the desired position.

23S.N.P.I.T. & R.C.

Detailing

24S.N.P.I.T. & R.C.

Limit state method In this method of design, the structure shall be

designed to withstand safety all loads liable to act on it throughout its life. It shall also safety the serviceability requirements, such as limitations on deflection and cracking.

The aim of design is to achieve acceptable probabilities that the structure will not become unfit for use for which it is intended, that is, that it will not reach a limit state.

All relevent limit state shall be considered in designed to ensure an adequate degree of safety and serviceability. In general, the structure shall be designed for the most critical limit state and shall be checked for the other limit states. 25S.N.P.I.T. & R.C.

The limit state design philosophy, uses a multiple safety factor format, which attempts to provide adequate safety at ultimate loads as well as adequate serviceability at service loads, by considering all possible limit states.

For ensuring the above objectives, the design should be based on characteristics values for material strengths and applied loads, which takes into account the variation in the material strength and in the loads to be supported.

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Serviceability Limit States:• Cracking• Excessive Deflection• Buckling• Stability

Limit States

S.N.P.I.T. & R.C.

Working stress method: This is the traditional method of design, used not

only reinforced concrete but also for structural steel and timber. This method of design was evolved around the year 1900. this method was accepted by many national codes. This method is based on linear elastic method.

This method ensures adequate safety by suitably restricting the stresses in the materials induced by the expected working loads on the structure.

In this method it is assumed that concrete and steel are elastic. At the worst combination of working loads, the stresses in materials are not exceeded beyond permissible values.

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The permissible stresses are found out by using a suitable factor of safety to material strength, e.g. for concrete in compression due to bending, a factor of safety equal to 3.0 is considered on 28 days. Characteristic strength and factor of safety equal to 1.8 is considered on the yeild strength for mild steel reinforcement in tension due to bending.

Working stress method does not consider the mode of failure of the structure . Also, the reserve strength of materials beyond yield point is not considered in this method of design.

The WSM assumes strain compatibility, whereby the strain the reinforcing steel is assumed to be equal to that in the adjoining concrete to which it is bonded.

29S.N.P.I.T. & R.C.

Demerits of WSM:

The WSM does not show the real strength nor gives the true factor of safety the structure under failure.

Because of creep and non linear stress- strain relationship , concrete does not have definite modulus of elasticity.

It assumes stress-strain relationship for concrete is constant, which is not true

WSM does not consider the mode of failure of the structure i.e. ductile or brittle.

It give large sections of structural elements, thus uneconomical.

30S.N.P.I.T. & R.C.

Merits of WSM:

It is simple, both in concept as well as in application.

The design usually results in large sections of structural members, compared to LSM. Due to this, structures designed by WSM give better serviceability performance. i.e., less deflection, less crack width etc.

It is reasonably reliable.

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Engineering

design philosophy in structure design in civil engineering