EFFECTS OF USING LOWER STEEL GRADE ON THE CRITICAL MEMBERS TO THE SEISMIC PERFORMANCE OF STEEL TRUSS BRIDGE STRUCTURES

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 10, October 2017, pp , Article ID: IJCIET_08_10_099 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed EFFECTS OF USING LOWER STEEL GRADE ON THE CRITICAL MEMBERS TO THE SEISMIC PERFORMANCE OF STEEL TRUSS BRIDGE STRUCTURES Ming Narto Wijaya Civil Engineering Department, Brawijaya University, MT. Haryono street 167 Malang East Java, Indonesia Lilya Susanti Civil Engineering Department, Brawijaya University, MT. Haryono street 167 Malang East Java, Indonesia Desy Setyowulan Civil Engineering Department, Brawijaya University, MT. Haryono street 167 Malang East Java, Indonesia Ahmad Agus Salim Civil Engineering Department, Brawijaya University, MT. Haryono street 167 Malang East Java, Indonesia ABSTRACT This paper investigated the effect of using lower steel grade material on the critical members of steel truss bridge structure to their maximum stress and strain. Full truss bridge structure with uniform and not uniform steel grade on their critical members were used as the present models. Two direction earthquake motion were applied on the bridge supports. Results indicated that using lower steel grade in the critical members in the truss bridge resulted higher strength reduction in carrying earthquake load than any other parts in the steel truss bridge structure. Key words: Seismic performance, steel grade, maximum stress, truss bridge structure. Cite this Article: Ming Narto Wijaya, Lilya Susanti, Desy Setyowulan and Ahmad Agus Salim, Effects of using Lower Steel Grade on the Critical Members to the Seismic Performance of Steel Truss Bridge Structures. International Journal of Civil Engineering and Technology, 8(10), 2017, pp

2 Ming Narto Wijaya, Lilya Susanti, Desy Setyowulan and Ahmad Agus Salim 1. INTRODUCTION Truss bridge structures are often used as the short span bridges. Truss bridge is a combination of truss elements which form triangular shape. In each certain period, the truss elements have to be repaired to maintain their structural capacity. In the repairment, sometimes they need to be replaced with the new steel material. If they are replaced with the different steel grade materials, it could affect the structural capacity. Previous study by Widjajakusuma J and Wijaya H observed the effect of geometries on the natural frequencies of Pratt truss bridge structure. In here, the results show that the natural frequency decreased by the increasing of the span number. The damaged of the bearing pad also affected the natural frequencies of the bridge structure [1]. Earthquake is a big problem for Indonesian citizen because this country located in the boundary of earth tectonic plates which means that everytime the earth plate move, it results an earthquake. Sometimes it occurred in the small magnitudes but sometimes in the very big richter scale. Hence, every structure in Indonesia have to be designed to resist the earthquake loads. Indonesian country is divided into 6 earthquake zona according to Indonesian Standard for Designing Earthquake Resistant in The Building Structures [2].That is why investigating seismic capacity of the truss bridge structures is very important in Indonesia. The best method to analyze the seismic performance of the steel truss brige sructures is dynamic analysis using time history method. Many previous studies have studied about this. Khuyen, H T and Iwasaki E have investigated an approximate method of dynamic amplification factor for alternate load path in reundancy and progressive collapse linear static analysis for steel truss bridges. This paper purposed an empirical equation that allows for the computation of the dynamic amplification factor for the maximum norm stress in static linear elastic analysis of the damaged model with a member removal [3]. Shibeshi R D and Roth C P studied the field measurement and dynamic analysis of a steel truss railway bridges. The study was approached by three different methods which are field measurement, modal analysis using three dimensional finite element model and simple generalized single degree of fredom [4]. Another study by Liang C Y and Chen A studied a method for examining the seismic performance of steel arch deck bridges. The result showed that the lateral earthquake motion has little effect on the displacement, axial force and bending moment responses of the arch rib [5]. As the previous study by Susanti L et. al. [6] mentioned the most critical members of the truss bridge structure located in the nearest location with the bridge supports, present study investigated the effect of replacing the critical members of the steel truss bridge structure with the lower steel grade to their structural capacity which means maximum stress and strain. To determine the steel grade, the steel material has to be tension tested. The result of this test are the stress-strain history which include the yield stress, maximum stress and modulus of elasticity. Research report by Rasmussen K J R [7] developed an expression for the stressstrain curves for stainless steel alloys which is valid over the full strain range. The equation is useful for the design and numerical modelling of stainless steel members and elements which reach stresses beyond the 0.2% proof stress in their ultimate limit state. In the numerical analysis, these stress and strain value have to be transferred into true stress and true strain. The research article by Arasaratnam P et. al [8] observed the true stress-true strain models for structural steel elements. In here, the true stress-true strain model parameters were established through a combination of experimental and numerical modeling techniques editor@iaeme.com

3 Effects of using Lower Steel Grade on the Critical Members to the Seismic Performance of Steel Truss Bridge Structures Using previous studies as references, the present study conducted two steps of research, experimental tensile test of steel material and dynamic numerical analysis of full truss bridge models to observe the maximum stress and strain in the edge and center beam of the truss bridge structure. The results could be used as references for engineers and researchers to apply and develop the seismic performance of the steel truss bridge structure especially. 2. METHODOLOGY 2.1. Tensile Test of Steel Materials Tensile test was conducted using Universal Testing Machine (UTM). The results of this test were yield stress and maximum stress. Present experimental research also used strain gauge as a tool to to collect the history of strain data in order to determine the modulus of elasticity of the steel members. The present tensile test specimens were taken randomly from some markets in Indonesia with the indication that some of them have lower steel grade compared with the requirement of steel grade according to Indonesian standard for designing steel structures [9]. The dimension and geometrical properties of the steel model followed the ASTM A370-03a Standard [10]. Present tensile test used 20 steel samples with th various geometrical properties such as canal section (4 specimens), WF section (4 specimens), angles section (4 specimens), rectangular hollow section (4 specimens) and plate section (4 specimens). Figure 1 shows the dimension of the steel samples following the ASTM A370-03a. Present study used L as 70 mm, A as 200 mm, B as 200 mm and w as 40 mm. Strain gauges were placed in the center steel specimens and connected with the data logger to read the strain history. Figure 1 Tensile test specimen following ASTM A370-03a 2.2. Dynamic Analysis of Truss Bridge Structure The next step in the present study was analyzing the full truss bridge model using the timehistory method. The dynamic analysis was conducted using ABAQUS/Standard numerical software [11]. Beam 31 was applied as present truss members element type. Truss configuration and also each section dimension were taken from the existing steel truss bridge structure in Malang, Indonesia named Soekarno-Hatta bridge. Present analysis used 2 steel truss bridge models (Figure 2). Model 1 with the uniform steel grade for all member (yield stress as 240 MPa, maximum stress as 370 MPa and modulus elasticity as MPa) and model 2 which used lower steel grade in the each of bottom and top edge member according to the result of tensile test in the previous chapter. Material input data was taken from the result of tensile test in the Chapter 2.1. The section properties of the steel members is shown in Table editor@iaeme.com

4 Acceleration (gal) Acceleration (gal) Ming Narto Wijaya, Lilya Susanti, Desy Setyowulan and Ahmad Agus Salim Table 1 Section property of the truss members Part Top beam members Bottom beam members Diagonal beam members Top cross beam members Bottom cross beam members Section property W360x134 W360x134 W360x134 W360x134 W700x115 (a) Model 1 (b) Model 2 Figure 2 Truss models in ABAQUS software Earthquake load input data was taken from Sumatra Island earthquake record (2010) as shown in Figure 3. Two direction earthquake motion which were North-South (NS) and East- West (EW) direction applied in the each bridge bearing pad. Two direction of earthquake motion placed in the pin support and one direction in the roll support. The output data from this dynamic analysis was the maximum stress and strain in the truss edge beams, bottom center beams and also top center beams Time (s) -400 Time (s) (a) EW direction (b) NS direction Figure 3 Sumatra Island earthquake data record 3. RESULTS AND DISCUSSION 3.1. Result of the Tensile Test Steel tensile test was conducted using Universal Testing Machine (UTM). The output from this tensile test were the load history and steel elongation which were transferred into stress and strain value. Result of the present tensile test is shown in Table 2. Indonesian standard for designing steel structure for buildings has stated that the minimum steel grade is BJ-34 with the yield stress as 210 MPa, maximum steel stress as 340 MPa and modulus of elasticity as MPa. According to the result of tensile test in Table 2, it can be conclude that around 38% of the specimens have the steel grade that under the requirement. The minimum value of yield stress, maximum stress and modulus of elasticity of the specimens then was used as material input data in the dynamic analysis of truss bridge structure in the next chapter editor@iaeme.com

5 Effects of using Lower Steel Grade on the Critical Members to the Seismic Performance of Steel Truss Bridge Structures Table 2 Result of the tensile stress Specimen σ yield σ max. E MPa MPa MPa Channel Channel Channel Channel Plate Plate Plate Plate RHS RHS RHS RHS WF WF WF WF Angles Angles Angles Result of Dynamic Analysis of Truss Bridge Structures Before conducting dynamic analysis of the truss structure, the damping ratio of the truss structure has to be determined. These damping ratio which were alpha (α) and beta (β) determined from The Eigen Value Analysis. From the result of this analysis α was determined as and β as The earthquake load was magnified until three times of the actual acceleration. An actual bridge structure has designed to carry the severe earthquake load. That is why the bridge structure has not collapse yet if the analysis used the actual magnitude of earthquake loads. The present study aimed to understand the maximum stress and strain of the truss structure. Hence, the earthquake magnitude was magnified three times. Edge part of the truss structure in model 2 used yield stress as MPa, maximum stress as 125 MPa and modulus elasticity as MPa as material input data according to the result of tensile test in the previous chapter. Result of stress and strain distribution of truss structure model 1 are shown in Figure 4 and Figure 5. Figure 4 Stress distribution of model editor@iaeme.com

6 Ming Narto Wijaya, Lilya Susanti, Desy Setyowulan and Ahmad Agus Salim Figure 5 Strain distribution of model 1 It can be proved form Figure 4 and Figure 5 that the critical members of the truss structure were located in the edge beams near the bridge bearing pad especially pin supports. In the deformed shape of truss structure, it can be seen that the truss little bit twisted due to the earthquake load. This phenomenon was not visible in the deformed shape of model 2 in Figure 6 and Figure 7. In there figures of model 2, the bridge collapse predominantly by flexural bending effect. By using lower steel grade in the edge members of truss structure in model, the edge members suffered more damage compared with the edge members in model 1. Figure 6 Stress distribution of model 2 Figure 7 Strain distribution of model editor@iaeme.com

7 Stress / σ (MPa) Stress / σ (MPa) Effects of using Lower Steel Grade on the Critical Members to the Seismic Performance of Steel Truss Bridge Structures The result of stress-strain history of Model 1 and 2 in the edge, bottom center and top center parts of the truss structure are shown in the Figure 8 and 9 respectively. From the stress-strain history of model 1 in Figure 8, The maximum stress of the edge beam has a much bigger value ( MPa) compared with the bottom center ( MPa) and top center part of the truss structure ( MPa). Has a good agreement with model 1, in model 2, maximum stress in the edge part as MPa also has much higher value compared with the bottom center part ( MPa) and top center part ( MPa) Model 1 - edge beam Model 1 - bottom center beam Model 1 - top center beam -400 Strain / ε Figure 8 Stress-strain history of model Strain / ε Model 2 - edge beam Model 2 - bottom center beam Model 2 - top center beam Figure 9 Stress-strain history of model 1 By replacing the edge parts of the truss structure with the lower steel grade, model 2 resulted the edge part stress 16% smaller than model 1. Maximum stress in the bottom and top center part of model 2 and model 1 were almost similar each other. It indicated that the center parts of the bridge were not affected by the steel grade replacement in the edge members of the truss bridge structure. 4. CONCLUSIONS From the tensile stress results, there was around 38% steel materials which have lower steel grade compared with the minimum steel grade mentioned in the Indonesian standard for designing steel structures (SNI ). But it did not represent the steel quality in Indonesia because it still need more research to prove this statement. From the results of the dynamic analysis, it can be proved that the critical members in the truss bridge structure located in the edge beam nearest with the truss bearing pad especially pin support. Moreover, by using lower steel grade in the edge members of the truss bridge structure, the structural capacity reduced 16% compared with the uniform steel grade in all editor@iaeme.com

8 Ming Narto Wijaya, Lilya Susanti, Desy Setyowulan and Ahmad Agus Salim members of the truss structure. The bottom and top center parts of the bridge were not affected by the replacing of lower steel grade in the edge part of the truss structure. REFERENCES [1] Widjajakusuma J and Wijaya H, Effect of geometries on the natural frequencies of pratt truss bridges. The 5th International Conference of Euro Asia Civil Engineering Forum (EACEF-5) Procedia Engineering,125, 2015, [2] Indonesian National Standardization Institution, Earthquake resistance design procedures for building and non-building structures SNI Jakarta, [3] Khuyen H T and Iwasaki E, An approximate method of dynamic amplification factor for alternate load path in redundancy and progressive collapse linear static analysis for steel truss bridges. Case Studies in Structural Engineering, 6, 2016, [4] Shibeshi R D and Roth C P, Field measurement and dynamic analysis of a steel truss railway bridge. Journal of South African Institution of Civil Engineering, 58(3), 2016, paper [5] Liang C Y and Chen A, A method for examining the seismic performance of steel arch deck bridges. Front. Archit. Civ. Eng. China, 4(3), 2010, [6] Susanti L, Kasai A and Miyamoto Y, Postbuckling behavior of welded box section steel compression members. International Journal of Civil Engineering and Technology (IJCIET), 6(4), 2015, [7] Rasmussen K J R, Full-range stress-strain curves for stainless teel alloys. Research Report No R811 The University of Sidney, [8] Arasaratnam P, Sivakumaran K S and Tait M J, True stress-true strain models for structural steel elements. International Scholarly Research Network Civil Engineering, Article ID [9] Indonesian Minister of Public Work, Procedures for designing steel structure for buildings SNI , Jakarta, [10] ASTM International, Standard Test Methods and Definitions for Mechanical Testing of Steel Products ASTM A370-03a, West Conshohocken, [11] Dassault Systems Simulia Corp., ABAQUS/standard student edition Ver. 6.14, Providence, RI, USA, [12] Anusha Kudumula, Dr. Vaishali G Ghorpade and Dr. H. Sudarsana Rao, Seismic Performance of RC Framed Buildings Under Linear Dynamic Analysis. International Journal of Civil Engineering and Technology, 8(1), 2017, pp [13] Sandeep Ghosh and Dr. Shanmuga Sundaram M, Seismic Performance of RC Framed Irregular Buildings. International Journal of Civil Engineering and Technology, 8(4), 2017, pp editor@iaeme.com