1. INTRODUCTION:
In Every aspect of human civilization we needed structures to live in or to get what we need .But it is not only building structures so that it can fulfill the main purpose for what it was made for. Here comes the role of civil engineering and more precisely the role of analysis of structure. There are many classical methods to solve design problem and with time new software`s also coming into play. Here in this project work recent fem based software named SAP 2000 7.40, STAAD pro v8i has been used. Modern design offices are generally equipped with a wide variety of structural analysis software programs, invariably based on the stiffness matrix method. These Finite Element Analysis packages such as SAP 2000 7.40, STAAD pro v8i etc., give more accurate results compared with approximate methods, but they involve significant computational effort and therefore cost.
2. EASE OF USE
All real physical structures, when subjected to loads or displacements, behave dynamically. The additional inertia forces, from Newton’s second law, are equal to the mass times the acceleration. If the loads or displacements are applied very slowly then the inertia forces can be neglected and a static load analysis can be justified. Hence, dynamic analysis is a simple extension of static analysis. In addition, all real structures potentially have an infinite number of displacements.
Therefore, the most critical phase of a structural analysis is to create a computer model, with a finite number of mass less members and a finite number of node (joint) displacements that will simulate the behavior of the real structure. The mass of a structural system, which can be accurately estimated, is lumped at the nodes. Also, for linear elastic structures the stiffness properties of the members, with the aid of experimental data, can be approximated with a high degree of confidence. However, the dynamic loading, energy dissipation properties and boundary (foundation) conditions for many structures are difficult to estimate. This is always true for the cases of seismic input or wind loads. To reduce the errors that may be caused by the approximations summarized in the previous paragraph, it is necessary to conduct many different dynamic analyses using different computer models, loading and boundary conditions. It is not unrealistic to conduct 20 or more computer runs to design a new structure or to investigate retrofit options for an existing structure.
3. MODAL RESPONSE EQUATIONS
The most conservative method that is used to estimate a peak value of displacement or force within a structure is to use the sum of the absolute of the modal response values. This approach assumes that the maximum modal values for all modes occur at the same point in time.
Another very common approach is to use the Square Root of the Sum of the Squares, SRSS, on the maximum modal values to estimate the values of displacement or forces. The SRSS method assumes that all of the maximum modal values are statistically independent. For three-dimensional structures in which a large number of frequencies are almost identical, this assumption is not justified.
The relatively new method of modal combination is the Complete Quadratic Combination, CQC, method that was first published in 1981. It is based on random vibration theories and has found wide acceptance by most engineers and has been incorporated as an option in most modern computer programs for seismic analysis. Because many engineers and building codes are not requiring the use of the CQC method, one purpose of this chapter is to explain by example the advantages of using the CQC method and illustrate the potential problems in the use of the SRSS method of modal combination.
The peak value of a typical force can now be estimated from the maximum modal values using the CQC method with the application of the following double summation equation:
(2.8)
Where, fn is the modal force associated with mode n. The double summation is conducted over all modes. Similar equations can be applied to node displacements, relative displacements and base shears and overturning moments.
The cross-modal coefficients, ρnm, for the CQC method with constant damping are:
(2.9)
Where, 
and must be
equal to or less than 1.0. It is important to note that the cross-modal
coefficient array is symmetric and all terms are
positive.
4. RESPONSE SPECTRUM METHOD
Shall be performed using the design spectrum specified in IS 1893 (Part 1) : 2002 or by a site specific design spectrum in the same code. The basic mode superposition method, which is restricted to linearly elastic analysis, produces the complete time history response of joint displacements and member forces because of a specific ground motion loading. There are two major disadvantages of using this approach. First, the method produces a large amount of output information that can require an enormous amount of computational effort to conduct all possible design checks as a function of time. Second, the analysis must be repeated for several different earthquake motions to ensure that all the significant modes are excited, because a response spectrum for one earthquake, in a specified direction, is not a smooth function. There are significant computational advantages in using the response spectra method of seismic analysis for prediction of displacements and member forces in structural systems. The method involves the calculation of only the maximum values of the displacements and member forces in each mode using smooth design spectra that are the average of several earthquake motions. In this project the CQC method to combine the maximum modal response values to obtain the most probable peak value of displacement or force. In addition, it will be shown that the SRSS and CQC methods of combining results from orthogonal earthquake motions will allow one dynamic analysis to produce design forces for all members in the structure. CQC method of combination is used for structures having closely spaced modes. In the other direction, SRSS method is used for structures which do not have modes closely spaced. i.e. CQC method is therefore used. For three-dimensional seismic motion, the typical modal written as:
(2.1)
Where, the three Mode
Participation Factors are defined by 
in which i is equal to x,
y or z. Two major problems must be solved to obtain an approximate response
spectrum solution to this equation. First, for each direction of ground motion,
maximum peak forces and displacements must be estimated.
Second, after the response for the three orthogonal directions has been solved, it is necessary to estimate the maximum response from the three components of earthquake motion acting at the same time. This section addresses the modal combination problem from one component of motion only. For input in one direction only, Equation (2.1) is written as:
(2.2)
Given a specified
ground motion 
damping value and assuming 
it is
possible to solve Equation (2.2) at various values of ω and plot a curve
of the maximum peak response 
For this acceleration input,
the curve is by definition the displacement response spectrum for
the earthquake motion. A different curve will exist for each different value of
damping.
A plot of 
is defined
as the pseudo-velocity spectrum and a plot of 
is defined as the pseudo-acceleration
spectrum.
The three curves–displacement response spectrum, pseudo-velocity spectrum, and pseudo-acceleration spectrum–are normally plotted as one curve on special log paper. However, the pseudo-values have minimum physical significance and are not an essential part of a response spectrum analysis. The true values for maximum velocity and acceleration must be calculated from the solution of Equation (2.2).
There is a mathematical relationship, however, between the pseudo-acceleration spectrum and the total acceleration spectrum. The total acceleration of the unit mass, single degree-of-freedom system, governed by Equation (2.2), is given by:
(2.3)
Equation (2.2)
can be solved for 
and substituted into Equation
(2.3) to yield:
(2.4)
Therefore, for
the special case of zero damping, the total acceleration of the system is equal
to 
For
this reason, the displacement response spectrum curve is normally
not plotted as modal displacement 
versus ω. It is standard
to present the curve in terms of S(ω) versus a period T in
seconds, where:
and 
(2.5)
The
pseudo-acceleration spectrum curve, 
has the units of acceleration
versus period that has some physical significance for zero damping only. It is
apparent that all response spectrum curves represent the properties of the
earthquake at a specific site and are not a function of the properties of the
structural system. After estimation is made of the linear viscous damping
properties of the structure, a specific response spectrum curve is selected.
5. RESULTS AND GRAPHS
STAAD. Pro V8i is the most popular structural engineering software product for 3D model generation, analysis and multi-material design. It has an intuitive, user-friendly GUI, visualization tools, powerful analysis and design facilities and seamless integration to several other modeling and design software products. The software is fully compatible with all Windows operating systems but is optimized for Windows XP. SAP2000 is available in three commercial versions (Standard, PLUS, and Nonlinear)
5.1 CONCLUSION FROM OUTPUT OF SAP AND STAAD
Some of the conclusions came out from the output of graphs and analysis is described below:
1)We have shown some of the graph of mode shapes the Value of Eigen vector describes how much differences we got from each mode of vibration. At mode 3 and 4 the graph of Eigen vector is approximately same in SAP and STAAD.
2)SAP has done response spectrum analysis but not done the design of the structures but STAAD have done both analysis and design. Earlier versions of SAP may have the design option.
3)The joint reaction graph shows that the values (SAP and STAAD joint reaction) came out from output will be approximately same.
4)The notation of numbering of column and beam element will be different in both the software’s. That’s why its difficult to identify the nodes and also SAP and STAAD have different axes direction so its little confusing when solving.
5)The values of no. of mode should be increased as we going to higher structure so as frequency and period should be divided and reduced to the required no. of modes.
5)Modeling in STAAD is easier then SAP and also STAAD have advance features then SAP. Some new version of SAP will have features like STAAD.
6)If we copy any beam or column to any distance their property and loading is also copied in STAAD but in SAP we have to reenter the loading after copying of any elements.
7)We have plot graph between joint reactions in another direction for verification of results and it verified the reactions.
8)In our project we have not used steel section but yet STAAD have parallel flange section tables for steel structure and also having I.S. 800-2007 steel code which is not in SAP software’s.
1)STAAD have Steel, 37 codes from around the world including AISC 360-05. Concrete, 25 codes batch processed or within the interactive RC design modes. Timber, 4 design codes supported. Aluminum, stainless steel, composite floors, and cold-forms design checks. Shear wall designs for US, Indian and British codes.
2)SAP has AISC-ASD89, AISC-LRFD94, AASHTA LRFD 97, BS5950-90, CAN/CSA-S16.1.94, and EUROCODE 3 ENV 1993-1-1 codes for steel structures.
5.2 RECOMMENDATIONS FOR FUTURE WORK
In the project we have analyzed the structure with finite element based software’s SAP and STAAD. In future we can analyze the structure by some more software’s like TEKLA, SAP 2000 Nonlinear version 13, STAAD 2009 etc. We have done the dynamic analysis on the buildings with Ground +four and six storied building there are some changes in the values came from software’s and in actual so from my consideration I have chosen to take a model analysis so that I can insure on my results that the values from the output and in actual will be same. It will do by the help of structure model having same nature as in real structure and vibration table with frequency adjustments and time response. It can be done by taking the model on the vibration table and the frequency require can be adjusted. And note the periods and mode shapes so we can compare from actual and software’s output and classify the software efficiency.
Some other works for future recommendation are described below:
1)In the project graph between frequencies and time periods for different mode shapes can be compared.
2)The building used in the project will be of regular shape and size in zone IV; we can also take irregular shape of structure for analysis with different zones.
3)We can increase no. of elements (like beams and columns) for maximize no. of modes by using cutoff mode option.
4)We can also compare the result with other software’s like STRUDS 2007, TEKLA , PRIMA etc. so that we can insure that the output is equal/or not in any other type of software’s.
5)In the project we use the response spectrum method for analysis; we can also use time history method, free vibration method for design in different software’s as wel.
6)Fast nonlinear analysis is also another approach for analysis which is quite effective then response spectrum but not very much used and requires large programming software’s, so for skeletal with higher dynamic load affection being analyzed by this approach in future.
7)We can change the floor load ratio, it results us change in frequency and mode shapes. So that we can compare between our output to that output came.
8)We can also compare the dynamic analysis results to static analysis results with their design base shear. Also make a modification factor for the lateral loads acting on the structure.We can do the analysis by including shear wall and dampers in the frame so that it gives us reduction in frequency and lateral loads and also mode shapes.
6. REFERENCES:
1. Mario Paz, “Free vibrartion of a shear building using sap2000” 5TH edition in 2009.
2. Brebbia CA, Ferrante AJ. Computational Methods for Solution of Engineering Problems, 2nd Edition, Pentech Press, London: Plymouth, 1979.
3. Bryan Stafford Smith, Tall Building Structures, Alex Coull John Wiley and Co., Canada, 1991.
4. Clough, R.W. and Penzien, J. Dynamics of Structures. Second Edition, McGraw-Hill, 1994.
5. Coates RC, Coutie MG, Kong FK. Structural Analysis, 2nd Edition, ELBS/Van Nostrand Reinhold (U.K), 1986.
6. Anil k. Chopra “Dynamics of structures”.
7. Taranath BS. Structural Analysis and Design of Tall Buildings, 1st Edition, 1988.
8. Edward L. Wilson, “Three Dimensional Static and Dynamic Analysis of Structures” in January 2002.
9. Zhao HL, Wu ZZ, Liu JL. Experimental study, theoretical analysis and design of sheetframed spaced structures, In: Nooshin H, ed., 3rd International Conference on Space Structures. London: Elsevier Applied Science Publishers, 1984, pp. 219-24.
TECHNICAL / RESEARCH PAPERS and CODES
10. Michael H. Swanger Georgia Tech CASE Center GTSUG 2004 June 9-12, 2004 Boston, MA, “Dynamic Analysis Tips, Techniques, etc. New and Review”.
11. I.S. 1893 (Part 1):2002 Criteria for Earthquake Resistant Design of structures Part 1 General provisions and buildings, Draft of Fifth Revision, Bureau of Indian Standards, New Delhi, 2002.
12. www.bentley.com , “Product data sheet of STAAD PRO” and computer and structures university Avenue Berkeley, California,”SAP 2000 USER GUIDE”.
13. M. Ashraf*, Z.A. Siddiqi and M.A. Javed Asian journal of civil engineering (building and housing) vol.9 , no.5 (2008) pages 525-537 , “Configuration of a Multistorey Building Subjected to Lateral Forces”.
14. Computers and Structures University Avenue Berkeley, California SAP2000 Integrated Finite Element Analysis and Design of Structures Verification Manual 1995.
15. A.R. Chandrasekaran + and D. S. Prakash Rao Retired Professor, Department of Earthquake Engineering, IIT, Roorkee and Professor of Civil Engineering, University College of Engineering, Osmania University Aseismic “Design of Multi-storied RCC Buildings” Dec 2002.
16. Rahul leslie, Powerpoint presentation on “Seismic analysis of Multi-storied RC buildings part IV and V” in 1999.
Received on 08.11.2010 Accepted on 26.01.2011
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Research J. Engineering and Tech. 2(1): Jan.-Mar. 2011 page 01-04