P. Magudeaswaran et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945

Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/1061-1062

Research Paper PUSHOVER ANALYSIS OF STEEL FRAME

Dr.P.Eswaramoorthi1 P.Magudeaswaran2 A. Dinesh2

Address for Correspondence

1Professor, Department of Civil Engineering, Kumaraguru College of Technology, Coimbatore-49. 2Assistant professor, Department of Civil Engineering, Ramakrishna Institute of Technology, Coimbatore-49.

ABSTRACT: In the present scenario, Steel framed structures plays an important role in construction industry because they are cost efficient, sustainable, durable, ductile and safe. To analyze the structure under seismic loads, the deformed geometry and the non-linear behavior of the structure is to be considered. Hence to determine the performance of the structure, non-linear or pushover analysis is performed. The pushover testing has been carried out on two frames namely Bare frame and Steel braced frame. The research concentrates on a computer based push-over analysis technique and experimental analysis for performance-based design of steel framed structures. In this present study, nonlinear analysis of Steel frame using ANSYS 14.5 under the horizontal loading has been carried out and it is validated experimentally. It is evident that the yield load & ultimate load of Steel braced frame is greater than the bare frame and the deflection of the steel braced frame is less compared to the bare frame due to increase in its diagonal stiffness. The values are validated experimentally and by stiffness method of matrix analysis. KEYWORDS: Steel, pushover analysis, ANSYS, bare frame, braced frame.

1. INTRODUCTION The Indian Construction is often guided by steel, cement as the prime material of construction. Cement requires a healthy partnership with aggregates and steel to form the structural element called concrete. Steel, on the other hand has an advantage of partnering with concrete and also can go alone as an individual structural element. Steel frames play an important role in construction industry because they are cost efficient, sustainable, durable, ductile and safe. Recently, the need for structural rehabilitation of civil infrastructures all over the world is well known and a great amount of research is going on this field. Every time new technology will develop which are changes in the contributing factors to structure such as increase in load requirement, corrosion deterioration to exposure to aggressive environments, changes in functionality, potential damaged caused by mechanical and environmental effects, increase in material strength and durability. Nowadays, steel frame system with beams and columns is become the conventional building structure in construction world. Structural design and structural analysis are both of the criteria needed to create a structure that safely accomplish its function in order to produce structures in a stability condition. The main advantage in steel frame is that, the post elastic behavior will occurs only in it. To analyze the structure under seismic loads, the deformed geometry and the non-linear behavior of the structure is to be considered. Hence to determine the performance of the structure, non-linear or pushover analysis is performed. Pushover analysis is the preferred analysis procedure for design and seismic performance evaluation purposes as the procedure is relatively simple and considers post elastic behavior. To analyse and evaluate the seismic performance of

1. Bare steel frame 2. Braced steel frame

by pushover analysis using ANSYS software and to validate it experimentally. The geometric and structural details of bare, braced are drafted using AutoCAD software. The non-linear pushover analysis was carried out to determine the behaviour of the frame by applying horizontal load at the top corner of the frame using ANSYS software. In experimental work, mat and formwork are prepared and deck slab is casted with the frames. After casting, load is applied

at the top corner of the beam and its behaviour is determined. Then the results from analytical and experimental investigations are compared. 1.1. Materials and Details of frame The geometric detail of bare frame and braced frame are 920mm X 50mm X 1050mm and 920mm X 50mm X 1050mm with 8mm dia rod respectively. The box section detail of both frames is 100mm X 50mm X4mm.The materials used for casting of deck slab are Coarse aggregate (25mm), fine aggregate (sand), 53 grade cement, binder, PVC pipe, U-Hook, Wood. The size of form work is 1240mm X 940mm. The deck slab is casted for M20 mix, which has the concrete mix of 1:1.5:3 and Water/Cement ratio of 0.5. Deck slab is casted along with frames for experimental investigations. 2. Analytical and Experimental Procedure A Frame is a structure made up from columns and beams that connected to each other at joints. Braced frame is a frame that has been supported by a bracing system to prevent it from sway when subjected to lateral loading. The installation of bracing system had provided more stability to system because it can resist the lateral loading from wind and earthquake. Analytical study on steel frame is carried out by ANSYS 14.5 software. Meshing element used is SOLID186 3D 20 – Node structural solid for both Bare frame and Braced steel frame. After meshing horizontal load and fixed boundary conditions are defined and behaviour of the frame is computed. In the experimental investigations, Deck slab is casted along with the frames and load is applied at the top and its behaviour is determined. 3. Results and Discussion 3.1 Bare frame In the analytical investigation, the unit system of the bare frame in the ANSYS 14.5 software is set as metric, deg and rad/s. The drafted bare frame is imported to the ANSYS 14.5 with length along X, Y and Z direction as 920mm, 1050mm and 50mm respectively. The bare frame is provided with a fixed support at its bottom and horizontal load is applied at top left corner of the frame and the deflection is computed for each load step. The bare frame is subjected to a horizontal load of 50kN, so that the frame gets deflected and the maximum deformation occurs at the top of the section. The deflected shape of Bare frame in ANSYS is shown in figure 1

P. Magudeaswaran et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945

Int J Adv Engg Tech/Vol. VII/Issue II/April-June,2016/1101-1103

Figure 1 Deflected shape of Bare frame in ANSYS

In the experimental investigation, the deck slab is casted with M20 mix. The deck slab strength is tested using Rebound hammer test. Once it attains sufficient strength, the frame can taken to the loading frame. Once the frame is shifted to testing position, the frame is subjected to lateral loading and its deflection is measured at its top and mid-height position using dial gauges. The deflected shape of bare frame in the experimental investigation is shown in figure 2.

Figure 2 Deflected shape of bare frame in experimental

investigation The deflection is noted for each load and the load – deflection curve is plotted. The results obtained are plotted in Table 1.

Table 1: Results of Bare frame Description Bare frame

An

alyt

ical

Yield load (kN) 36 Deflection @ yield load

(mm) 8.965

Ultimate load (kN) 45

Deflection @ ultimate load (mm)

100.53

Ex

per

imen

tal Yield load (kN) 41

Deflection @ yield load (mm)

12.695

Ultimate load (kN) 50

Deflection @ ultimate load (mm)

77.89

Figure 3 represents the analytical and experimental comparison of load – deflection of bare frame.

Figure 3 Load – deflection graph of bare frame

3.2 Braced frame In the analytical investigations, the unit system of the braced frame in the ANSYS 14.5 software is set as metric, deg and rad/s. The drafted bare frame is imported to the ANSYS 14.5 with length along X, Y

and Z direction as 920mm, 1050mm and 50mm respectively. The braced frame is provided with a fixed support at its bottom and horizontal load is applied at top left corner of the frame and the deflection is computed for each load step. The braced frame is subjected to a horizontal load of 60kN, so that the frame gets deflected and the maximum deformation occurs at the top of the section. The load – deformation values of braced steel frame is noted. The deflected shape of Braced frame in ANSYS is shown in figure 4

Figure 4 Deflected shape of Braced frame in ANSYS

In the experimental investigations, same procedure in Bare frame is carried out. During testing, the compression bracing rod is subjected to bending due to compression and the tensile bracing rod is subjected to elongation due to tension. The failure of the braced frame occurs due to the breaking of weld in the tensile rod. The deflected shape of braced frame in the experimental investigation is shown in figure 5.

Figure 5 Deflected shape of Braced frame in

experimental investigation The deflection is noted for each load and the load – deflection curve is plotted. The results obtained are plotted in Table 2.

Table 2: Results of Braced frame Description Braced frame

An

aly

tica

l Yield load (kN) 44

Deflection @ yield load (mm) 10.19 Ultimate load (kN) 57.6

Deflection @ ultimate load (mm) 36.96

Ex

per

imen

tal

Yield load (kN) 54 Deflection @ yield load (mm) 9.167

Ultimate load (kN) 85

Deflection @ ultimate load (mm) 25.237

Figure 6 represents the analytical and experimental comparison of load – deflection of braced frame.

Figure 6 Load – deflection graph of braced frame

0

10

20

30

40

50

60

0 50 100

LO

AD

(k

N)

DEFLECTION (mm)

LOAD - DEFLECTION GRAPH

ExperimentalAnalytical

0

20

40

60

80

100

0 10 20 30

LO

AD

(k

N)

DEFLECTION (mm)

LOAD-DEFLECTION GRAPH

Analytical Experimental

P. Magudeaswaran et al., International Journal of Advanced Engineering Technology E-ISSN 0976-3945

4. Comparative result After removal of load, deflection of the bare and braced are noted as 6.5 mm, 5.7mm.

Figure 7 Deflection of bare frame after removal of load

From the result it is understand that Due to the presence of Steel bracing in

frames, the diagonal stiffness of the frame is increased which in turn increase the yield strength and reduce the deflection in Braced steel frame compared to the Bare frame.

Compared to analytical values, yield load and ultimate load is increased and deflection is decreased in the experimental investigation which implies that use of ANSYS software in analysing the frame is feasible.

5. CONCLUSION The thorough investigation of the pushover analysis of steel frames such as bare frame, Braced frame are done. The Non-linear analysis of Steel frame using ANSYS and through experiment under the lateral loading has been carried out with the intention to investigate about the percentage of strength achieved. It is evident that the yield load of steel braced frame is 1.22 times greater than the yield load of bare frame in the analytical investigation and the yield load of steel braced frame is 1.32 times greater than the yield load of bare frame in the experimental investigation. Similarly, the ultimate load of steel braced frame is 1.28 times greater than the ultimate load of bare frame in the analytical investigation and the ultimate load of steel braced frame 1.07 times greater than the ultimate load of bare frame in the experimental investigation. At the ultimate load, Deflection of the Braced Frame is reduced 2.72 times compared to Bare frame in the analytical investigation and Deflection of the Braced Frame is reduced 3.09 times compared to Bare frame in the experimental investigation. The deflection value arrived through ANSYS is also validated by Stiffness method of Matrix analysis. REFERENCES:

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