EFFECTS OF DIFFERENT TRUCK LOADS ON BEHAVIOUR OF

Transcription

Journal of Engineering Science and TechnologyVol. 15, No. 6 (2020) 3836 - 3858 School of Engineering, Taylor’s UniversityEFFECTS OF DIFFERENT TRUCK LOADS ONBEHAVIOUR OF BRIDGES - A COMPARATIVE ANALYSISSUNITI SUPARP, PANUWAT JOYKLAD*Department of Civil and Environmental Engineering, Srinakharinwirot University Thailand*Corresponding Author: panuwatj@g.swu.ac.thAbstractDepartment of Highways, Thailand, has specified different weight conditions forThai trucks which are essentially different from other countries all over the world.The main objective of this study is to investigate the effect of different loadingconditions on the bridge response. Quantitative and qualitative analyses areconsidered in detail. The bridge responses due to loadings as per differentcountries were quantitatively compared with those of Thai loadings according toseveral government gazettes. The qualitative comparisons were descriptivelyexplained. In the quantitative analysis, bending moments and shear forces alongwith dynamic impact and the probability of lane occupation for different spanlengths (i.e., 5 m to 100 m) were determined. Based on analysis results, it wasfound that bridge response to the loading conditions of Thai trucks is very low ascompared with the loading conditions of other countries such as the United Statesof America, the United Kingdom, India, Japan and China. There was the onlyexception in the case of HS20-44. Further, it was observed that in the case ofshear and moment, there is an increase in the ratios with an increase in the spanlength of the bridges. The results indicate that the live load conditions of Thailandneed to be carefully considered in the design of highway bridges. The findings ofthe current study can be effectively utilized to implement the design strategies inThailand and the South-East Asian region.Keywords: AASHTO, Bridge, HL-93, Tandem, Thai trucks, Vehicles.3836

Effects of Different Truck Loads on Behaviour of Bridges - A Comparative . . . . 38371. IntroductionIt is widely known that truck loading conditions are very important to developdesign guidelines and standard codes for bridge design. For highway bridges,different loading conditions such as dead load, live load (both statically anddynamically), environmental load (such as temperature, wind and earthquake, etc.)and other loads (emergency braking, congestion and collision, etc.) are veryessential for safety and economical design [1-3]. The first two loading conditionssuch as dead and live load are usually referred to as the most fundamental loadingconditions. Usually, road bridges are designed in such a way to effectively carry allvehicular loads and are believed to be safe over their desired lifetimes [4]. Liveload conditions usually comprise different forces which are generated due to themovement of the vehicles over the bridges [5, 6].Many parameters may affect the distribution of live loads for bridges such aslength of span, the weight of trucks, axle loads and their configurations, vehicleposition on the bridge, amount of vehicles, the structural configuration of bridgesand usages of the vehicle on bridges. For the reason that the parameters for eachcountry are probably dissimilar, the highway bridge standard loadings of mostcountries have been developed gradually with slight regard to the existing standardsprevalent in other countries, even among neighbouring countries. Consequently, itis a basic need to know how the design live loadings for bridges of one countrydiffer from those of others.In Thailand, bridges are usually designed by following the design specificationsrecommended by the American Association of State Highway and TransportationOfficials standard specifications (AASHTO(STD)) [7]. However, the weightdistributions for Thai trucks as recommended by the Department of Highways(DOH) and the Department of Rural Roads (DRR) are different from those ofAASHTO(STD). DOH and DRR have issued many gazettes and declarations forthe legal total truck weights, distribution and configuration of axle loads [8-14]. Inpractice, bridge responses from specified Thai trucks are usually determined bymultiplying AASHTO(STD) live loads with certain correction factors. Theprevious studies showed that the correction factors were derived from simplysupported beams and continuous beams with several span lengths [15-20].Furthermore, AASHTO has recently provided new design provisions using theLoad and Resistance Factor Design (LRFD) method, (AASHTO(LRFD)), forcurrent highway bridge design practices [21, 22]. In the past, different researchershave investigated the correction factors by comparing the responses of differentbridges considering the loading specifications of Thai trucks with AASHTO liveloadings. However, in most of these studies, the dynamic effect due to the loadingspecifications of Thai trucks and AASHTO live loadings were considered being thesame. Also, in existing studies, single-lane load distribution was only consideredfor the analysis of vehicles and the factors due to the multiple lane load were notconsidered. Further, a detailed review of existing literature indicates that socomparison of bridge response to Thai trucks is only made for the standard loadingconditions of the United States of America.Barker and Puckett [22] 2005 and Tabsh and Tabatabai [23] 2001 investigatedthe effects of axle load configurations, distribution of weights of AASHTO(STD)live loadings or HS20-44 on the design of highway bridges. The authors reportedthat under moving load conditions, safety margins for highway bridges areJournal of Engineering Science and TechnologyDecember 2020, Vol. 15(6)

3838S. Suparp and P. Joykladinsufficient for a particular type of bridge, span length and type of truck. Further, itwas recommended by the authors to properly calibrate the standard specificationsof design loads to reveal the more accurate and realistic response of the highwaybridges for certain regions and areas [23-37]. In another study, Sritanet andAttasaeranewong [24] carried out a comparative study on bridge responseconsidering loading conditions due to Thai truck convoys with HS20-44 in orderto study the safety of girder-type highway bridges. In the comparative study, thelive load from Thai trucks was considered in different seven configurations andseventy-two characteristics in accordance with recommendations of DOH.However, the longest span length of the bridge was considered as 37.16 m. Theresults indicated that ultimate stresses in bridge girders are 26% and 23% higherdue to the semi-trailer of total weight 38 Ton and trailer of total weight 35 Ton,respectively, as compared with HS20-44. These values conformed to the valuewhich DOH recommended increasing up to 30% of the responses evaluated fromHS20-44. Vivithkeyoonwong and Rimdusit [25] investigated the effects ofdifferent truck loading conditions by considering trucks with different total loadssuch as 21 Ton, 26 Ton, 28 Ton and 35 Ton. In addition, the loading conditions ofHS20-44 were comparatively considered. For the analysis proposes, the spanlengths were varied from 10 m to 38 m. The research results indicated that, for shortspan bridges (i.e., span length less than or equal to 15 m), the loading conditions ofHS20-44 can be effectively used for the design of bridges in Thailand instead oftrucks with a total load of 21 Ton. However, for large spans (i.e., 38 m), the ultimatestresses due to considered loads were 95% higher than those of HS20-44. Further,in the case of truck loads with 28 Ton and 35 Ton, the ultimate maximum stresseswere found 171% and 238% higher than those from HS20-44, respectively.The literature review indicates that current research efforts are very beneficialto improve the design guidelines in Thailand. However, in the existing researchactivities, relatively shorter span lengths were considered. In addition, modern andlatest types of trucks are not investigated in detail. Recently, Suparp and Joyklad[15, 17] studied the highway bridge responses from simply supported beam systemwith different span lengths (i.e., 5 m to 60 m) due to HS20-44 and Thai trucks.Similarly, the longest span bridges, i.e., 90 m to 180 m for continuous beam systemswere also considered [16, 18]. Extensive research efforts had also been conductedin the past to compare the ultimate shear and bending moments due to the loadrecommendations of Thai trucks issued by DOH and DRR [8-14] with HS20-44.Based on the research efforts, different ratios of bridge responses were proposedfor highway bridges having several span lengths. These ratios can also beconsidered as the multiplier factors for HS20-44, thus it is possible to compare thecalculated bridge response to loading conditions of Thai Trucks. Although existingresearch data is very useful to evaluate the bridge response, most of the existingstudies only considered standard specifications of AASHTO(STD). Further,Suparp and Joyklad [19] 2011 investigated the response ratios of simple beambridges due to Thai trucks and HL-93 as specified in AASHTO(LRFD). The resultsindicated that various bridge span length, the shear ratios and the moment ratios arevaried from 0.89 to 1.34 and 0.90 to 1.25, respectively. For bridge design practicein Thailand, these ratios could be applied as a multiplier to HL-93.The main objective of the current study is to investigate and compare the effectsof different live load conditions on the structural responses of the bridge. In theanalysis, two different approaches, quantitative and qualitative, are employed toJournal of Engineering Science and TechnologyDecember 2020, Vol. 15(6)

Effects of Different Truck Loads on Behaviour of Bridges - A Comparative . . . . 3839achieve the research objectives. Research parameters mainly included are live loadconditions and span lengths of the bridge. The bridge responses due to loadings ofvarious countries are quantitatively compared with those of Thai loadingsaccording to several government gazettes. In the quantitative analysis, bendingmoments and shear forces along with dynamic impact and the probability of laneoccupation for different span lengths (i.e., 5 m to 100 m) are determined. Thedynamic impact effects due to live loads and the likelihood of lane occupation aredistinctly considered in the bridge response analysis for different standards. Theanalytical results are very useful to effectively carry out the more economical andsafety design of bridges and to implement the standard loading conditions forThailand and the South-East Asian region.2. Highway Live Loadings for Bridge Design2.1. Truck loads in ThailandIn 2005, DOH issued official gazettes in which specifications, load distributionsand weight limits of different Thai trucks were precisely rated and affirmed.Basically, three different types of highway vehicles were specified: 1) a single unitvehicle or a truck, 2) a truck with a semi-trailer, 3) a truck with a full-trailer asshown in Fig. 1. Additionally, DRR also specified vehicle types that were able tomove on the responsible roads. According to the DRR declaration [14], the detailsof weight limits and truck configurations were quite similar to those announced byDOH. Later on, during 2007-2008, DOH issued some additional official gazettesin which more precise specifications were provided to consider heavily overloadedof special vehicles or trucks on highway bridges. In 2009-2011, a detaileddescription of gross and axle weights for each type of vehicle was also consideredin the additional gazettes. In Fig. 1, S is the distance between the 1st axle of a semitrailer and kingpin of its truck. The distance S was specifically revised and variedfor different kinds of axle loads in the additional gazettes. Considering all officialgazettes issued by DOH (during 2005-2011), Thai trucks can be categorized as; 4single trucks, 26 semi-trailer trucks and 14 full-trailer trucks.In this study, it was proposed to consider only those vehicles which are speciallyused in normal traffic with three different conditions such as; 1) the vehicle havinghighest load will be considered in case of similar vehicle configurations, 2) thevehicle with shortest axle distance will be selected in case that weight of eachvehicle is equal, 3) all those vehicles which are revoked by declarations ofDecember 2012 are not considered. With these conditions, two single type trucks,nine semi-trailer trucks and four full-trailer trucks were included in the analysis[15]. The details of selected trucks are provided in Tables 1 to 3. Since the axledistance was not precisely mentioned in the declarations, therefore, the axledistances were collected from different truck suppliers and manufacturers [17].In the standard specifications of AASHTO(STD) [7: Appendix B], Thai trucksare arranged in the form of a convoy of trucks in such a way that the rear axle of thefront vehicle and the front axle of the successive vehicle is 9.14 m (30ft). Further,truck train loading is considered as a combination of 100% and 75% weight for aparticular type of truck as shown in Fig. 2. In this study, bridge responses aredetermined from each similar Thai truck arranged into a convoy. The analysis wasrepeated for every type of Thai truck. Subsequently, comparing with every load case,the maximum responses were considered as the enveloping values. Further, the liveJournal of Engineering Science and TechnologyDecember 2020, Vol. 15(6)

3840S. Suparp and P. Joykladload dynamic impact effect quantified in AASHTO(STD) was included in theanalysis. In addition, the impact allowances were considered as inverselyproportional to the bridge span length (where span length L in meters) and can becomputed using the expression as 15.24/(L 38) [7].(a) Single unit or truck.(b) Truck semi-trailer.(c) Truck full-trailer.Fig. 1. Three types of Thai truck vehicles.Fig. 2. Loading for truck train (Thai trucks): First truck 75%,second truck 100%, third 75%, and 75% for the fourth and the next

HS20-44. Vivithkeyoonwong and Rimdusit [25] investigated the effects of different truck loading conditions by considering trucks with different total loads such as 21 Ton, 26 Ton, 28 Ton and 35 Ton. In addition, the loading conditions of HS20-44 were comparatively