EXPERIMENTAL STUDY ON LINK SLAB FOR HIGHWAY GIRDERS

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1 การประช มว ชาการว ศวกรรมโยธาแห งชาต คร งท ๑๐ ชลบ ร ๒ ๔ พฤษภาคม ๒๕๔๘ EXPERIMENTAL STUDY ON LINK SLAB FOR HIGHWAY GIRDERS Tayagorn Charuhaimontri 1 Ekasit Limsuwan 2 1 Ph.D.Student, Department of Civil Engineering, Chulalongkorn University, Bangkok 10330, Thailand, Chanwut.C@student.netserv.hula.a.th 2 Professor, Department of Civil Engineering, Chulalongkorn University, Bangkok 10330, Thailand, feels@kankrow.eng.hula.a.th ABSTRACT : Most of highway onstrutions in Thailand are prefabriated onstrution omprising preast members inorporated with ast in-situ slab dek. Continuity of the dek an be treated to eliminate gaps between adjaent spans providing smooth riding with link slab. The link slab would aommodate all movements into the struture by means of axial deformation, rotation and translation an be interation of strutural behavior between adjaent spans. Therefore, in this paper the behavior of link slab with lap reinforement under yli loading was observed for rak distribution, rak width, load-defletion relationship and ultimate strength through experimental work onsidering variable length of lap reinforement whih an be lassified to 3 types of detailing. All speimens failed in shear mode but have different raking behavior. Also numerial results by means of the 3-dimensional nonlinear finite element method using the miroplane model (MASA3) and truss model were ompared with those of experimental results. The results would be the prinipal parameters for further design approah. KEYWORDS : Link slab, Highway girder, Reinforement detailing, Nonlinear finite element method 1. Inrodution Most of highway onstrution are now prefabriated onstrution omprising preast members, fabriated on site and then provide ast-in-situ slab dek on site. The preast girder is partiularly advantageous to permit large volume of prodution in short period, uniformed and systemati quality ontrol, and eretion with little or no interferene with the traffi. There are many types and setions of preast onstrution, the most ommon used in Thailand are I, T, U setion and the box-setion whih normally pratise with their appropriate span length and eretion equipment. In urrent pratie, eah span is usually onstruted to separate for individual span and provide expansion joint for eah single span. Continuity of bridge dek to eliminate gaps between adjaent spans supports is desirable to improve appearane and riding quality, to redue vibration and noise problems, to improve long term servieability, aesthetis, and safety, to prevent drainage of dek surfae through joint as for improving durability, to eliminate initial ost of joints and their subsequent maintenane, and to improve overall safety as ontinuous struture where redistribution of moments an be aented. However, there still be some limitation depended on many fators affeting girder movements due to loads and the servieability. In reent years, expansion joints have been eliminated to redue its number throughout total length of overall onstrution espeially for new bridges. The joints an be eliminated by providing ontinuous dek as whih girders an still be simply support and the joint an be eliminated by proper measures to enounter among ompliated interations in the region. The setion of the dek STR - 64 onneting the two adjaent simple-span girders is alled link slab as shown in fig 1. The riteria of providing link slab as ontinuous dek would aommodate all movements into the struture by means of translation, rotation, deformation and settlement as boundary ondition ounterat with strutural behavior of adjaent spans. Those onstraints will be affeted not only for prinipal behaviors but also the seondary stresses due to thermal, moisture, settlement, posttensioning, and some others. Those onditions are omplex in the behaviors whih are related to the auraies and its degree of reliability on strength, servieability and durability. Link slab problems were produed not only by movement of adjaent girders resulting from prestressing fore, loads, reep, shrinkage, thermal effet, foundation settlement, and bearing pad effet, but also by link slab suh as wheel load. So the theoretial model to study this problem must be modeled the boundary ondition and ause of link slab. From these effets, the link slab behavior will be non-linear aused by raking and material properties whih must be taken are in the study. The link slab is assumed to be flexible in omparison with end stiffness of the girders. Both ends of the slab are subjeted to vertial and longitudinal movement due to the modulus of elastomeri bearing pad and also subjeted to longitudinal and rotational movement due to girder movements. 2. Experimental works The behavior of link slab under yli loading was observed for rak distribution, rak width, loaddefletion relationship and ultimate strength through

2 experimental work onsidering variable length of lap reinforement whih an be lassified to 3 types of detailing. 2.1 Test Speimen In order to study the influene of reinforement detailing, 3 RC link slab speimens were tested. The speimens were designed to be possible for onstrution with a span of 2,000 mm and slab thikness of 200 mm (Fig 2). The support of link slab is designed to be fixed beause the stiffness of girder is muh more than stiffness of link slab and it is designed to be produed both positive and negative moments in link slab in order to simulate the behavior of link slab whih has to resist both moments. The measured dimensions of speimens are summarized in table 1. The length of lap reinforement was parameters in this test and the speimens detailing and name were shown in Fig 2 and table 1. The link slab speimens were tested under point load whih is applied using a survo-pulser multi-jak atuators of 100 tons apaity. The load is transmitted through a retangular steel plate of size 50 m x 20 m x 2 m to the link slab in order to represent the AASHTO HS20-44 standard truk wheel load. 2.4 Results The first raks of all speimens were flexural raks whih ourred at supports and mid span. Fig 4 shows the rak patterns and failure modes of all speimens. Table 2 summarized main test results on raking loads, rak sizes and failure loadsdisplaements. The maximum defletions under yli fatored wheel load were the same. Fig 5 shows the relationship between mid-span load and vertial displaement of link slab speimens. In the figure, it ould be onfirm that the detailing of link slab affeted the stiffness, rak distribution, rak width. The magnitude of the stiffness was inreased as the amount of reinforement in the speimen was inreased and fore distribution of struture. LS_000_S speimen ated as a antilever slab after mid-span raking so the mid-span defletion of this speimen is more than LS_025_S and LS_183_D respetively. LS_025_S speimen ated as semi-antilever slab whih an be observed from the out-of-plane defletions at three points along the mid-setion, at one-sixth span and at supports. The stress in reinforements are not yielded before shear failure. Shear rak was started from mid depth and then rak was immediately propagated through its depth until failure. 2.2 Materials In this study, ready-mixed-onrete was used and the harateristi ompressive strength of onrete is 300 ks. The used reinforements were DB16 and DB20 of whih yield strength were 4000 ks. Twenty eight days strength of onrete was measured using the standard speimen for asting onrete as shown in Table 1. Tests were onduted at 28 days after asting. 2.3 Test proedure and Measurements The overview of the test setup is shown in fig 2. Eletrial resistane strain gages of length 0.5 m are fixed aross the mid setion and edge setion of link slab on both top and bottom reinforements in order to measure the tensile and ompressive strains. Out-of-plane defletions at three points along the mid-setion, at onesixth span and at supports are measured by using linear variable defletion transduers (LVDT). During testing, LVDT, load ell and strain gauges signals were input to a omputerized data aquisition system. The speimens were initially loaded gradually up to 1 ton and then the load is released in order to ensure the loading edges remained in proper ontat with the speimen. Then the speimens are yli loaded in the first range before and after raking to observed raking load and tension stiffening behavior. Next, they are loaded from zero to 9.3 tons and released bak to zero and repeated the yle five times in order to establish a base line urve. The 9.3 tons load represents the fatored load for the AASHTO standard HS20-44 truk wheel load (7.1 tons + 30% for impat). Finally they are loaded to failure. STR Numerial results by means of nonlinear finite element [5] The used program MASA3 has been developed by Josko Ožbolt at the Institute of Constrution Materials, University of Stuttgart. MASA is an abbreviation of Marosopi Spae Analysis. The finite element ode of MASA is based on the miroplane model, and possible to apply to 2-dimensional and 3-dimensional analysis of quasi-brittle materials [4]. The smeared rak approah is employed and the onstant stiffness method (CSM) is applied as a root finding method. Furthermore, the rak band approah is used in order to be independent of mesh dependeny. In the numerial model onrete is modeled with solid elements and reinforement is modeled with bar and beam element. Taking the symmetry into aount, only ¼ of the speimen has to be modeled. The load displaement relationship and rak patterns results from MASA3 is shown in fig 6,7. From the numerial results it shows a good results of rak patterns and failure loads ompared to testing results as shown in table Analytial results by means of truss model In reinfored onrete slab without transverse reinforement, the strutural behaviour is satisfatorily explained by the tooth model. The shear fore is mainly transferred in the raked tension zone of the member by the ombined ation of the frition along the rak faes and the dowel fore of the longitudinal reinforement. From the stress field between the raks is governed by an inlined biaxial tension-ompression field in the onrete. It is well represented by the simple truss model [6]. The allowable tensile strength for onrete ties is between 0.25 f (MPa) and 0.42 f (MPa) depended on

3 raking in ties. Using truss model and failure load from testing, the tensile strength for onrete ties are 0.26 f (MPa), 0.30 f (MPa) and 0.28 f (MPa) for LS_000_S, LS_025_S, LS_189_D respetively whih is in the range shown above. 5. Conlusion [1] The different reinforement detailings of link slab whih are possible for onstrution is affeted different fore distribution, stiffness, rak distribution and rak width whih is served for different ation from end girder boundary and different attempt to maintain link slab. [2] However all of the speimens are failed by shear mode, the link slab design is based on servieability and durability whih is deformation ontrol and rak ontrol. [3] Numerial results an estimate very good results of rak pattern and load-defletion urve ompared to test result. [4] Ultimate load of link slab is shear strength of slab without transverse reinforement whih an be predited from FEM and STM. Referenes [1] Charuhaimontri C., Limsuwan E., May 19-21, End Movement of Highway Girders, 9 th National Convention on Civil Engineering, v.1, pp. invited1-6. [2] Issam Harik, et al., May 23-27, Stati Testing on FRP Bridge Dek Panel, 44 th International SAMPE Symposium, pp [3] HyungKeun Ryu, SungPil Chang, YoungJin Kim and BongChul Joo, Deember 16-18, Experimental Works on Preast Conrete Deks with Loop Joints, 9 th EASEC, pp. RCS7-13. [4] Ožbolt, J.: MASA3, Finite element program for 3D nonlinear analysis strutures, MASA manual, Institute for Constrution Materials, University of Stuttgart, [5] Charuhaimontri C., Limsuwan E., Deember 13-15, Numerial Studies on Detailing of Link Slab for Highway Girder Considering Craking Behavior, 16 th KKCNN symposium on ivil engineering, pp [6] Karl-Heinz Reinek, Ultimate Shear Fore of Strutural Conrete Members without Transverse Reinforement Derived from a Mehanial Model, ACI Strutural Journal, v.88 No.5: pp Aknowledgement We would like to thank TRF (Thailand Researh Fund) for the finanial support of the Ph.D. study in Chulalongkorn University and DAAD (Deutsher Akademisher Austaush Dienst) for finanial support of the 6-months study at the University of Stuttgart, Germany. Figure 1 Link slab in highway girders Figure 2 Test speimen (LVDT and load arrangement) STR - 66

4 Figure 3 Speimens reinforement detailing: LS_000_S, LS_025_S, LS_183_D Table 1 Test speimens Name Average thikness (m) Level of upperlower reinforement (m) L M R L M R Average Conrete Strength (ks) Lap Length (m) Top reinforement Bottom reinforement LS_000_S DB16@10 DB16@10 LS_025_S DB16@10 DB16@10 LS_183_D DB20@10 DB16@10 Table 2 Test result, FEM result and STM result Speimens Craking load (T) Load(T) at rak width(mm) Failure load (T)displaement (mm) testing FEM LS_000_S LS_025_S LS_183_D * Note: * failure before this rak width STR - 67

5 Figure 4 rak pattern and failure mode of LS_000_S, LS_025_S, LS_183_D Load (Ton) Load-Displaement at midspan LS_000_S LS_025_S LS_183_D Displaement (mm) Figure 5 Load-displaement relationship from testing STR - 68

6 Figure 6 Crak pattern before failure (left) and at failure (right) of LS_000_S, LS_025_S, LS_183_D Load (Ton) Load-Displaement at midspan LS_000_S LS_025_S LS_183_D Displaement (mm) Figure 7 Load-displaement relationship from finite element method STR - 69