Terastorusildade kandevõimearvutused

Arvutustulemustest selgub, et SDM meetodi puhul osutub määravaks liikluskoormuseks pealiskihi paksuse 1,0…3,0 m juures KM1. Pealiskihi paksuse 0,5 m juures osutub määravaks koormuseks KM2. Samuti on näha, et liikluskoormuse KM3 mõju suureneb pealiskihi suurenemisega toru peal. Arvutustest võib järeldada, et KM3 võib osutuda määravaks suurte pealiskihi paksuste juures või suure laiusega terastorusilla puhul. Järeldus on tingitud asjaolust, et KM1 puhul on tegemist kaheteljelise veokiga, kuid KM3 korral on antud töös vaadeldud 18 telge. CHBDC meetodi arvutustes on määravaks koormuseks osutunud kõikidel juhtudel KM1, see on tingitud meetodi liikluskoormuse hajuvuse käsitlemisest. Sellest tulenevalt ei saa liikluskoormus KM3 osutuda antud töös uuritavate torude puhul määravaks ka suure pealiskihi paksuse juures. CHBDC meetod ei võimalda antud töös kõigi käsitletavate pealiskihi paksuste puhul arvutusi teostada, millest tingitult on meetodi kasutuskohad tugevalt piiratud. Kuna Eestis esinevat pinnareljeefi arvestades on pinnasetööde mahtude piiramise tõttu soositud pigem madalate pealiskihi paksuste kasutamine, ei võimalda CHBDC meetod nendes olukordades kandevõimearvutuste tegemist. Diplomitöö autor on arvamusel, et CHBDC meetodit ei ole Eestis piisavalt käsitletud ning on tõenäoline, et antud meetodit kasutades võib tekkida oht, kus meetodit kasutades eiratakse vähima ja suurima pealiskihi paksuse nõuet. Samuti ilmneb CHBDC meetodi rakendamisel tõsiasi, et meetod kasutab ühte konkreetset liikluskoormuse mudelit, mida eurokoodeksis ei käsitleta. Samas on Eestis kohustus kasutada eurokoodeksite koormusi ning seetõttu tuleb kombineerida kahte erinevatel alustel baseeruvat standardit, mis ei pruugi olla kooskõlas CHBDC meetodis liikluskoormustest tulenevate sisejõudude arvutamise kontseptsiooniga. Seetõttu on põhjust arvata, et CHBDC arvutusmeetodit ei tohiks eurokoodeksites kirjeldatud liikluskoormuste korral kasutada enne, kui on teostatud põhjalikum kahe arvutusmeetodi omavaheline võrdlusanalüüs. Vaadeldes kahe meetodi arvutuste tulemusel saadud terasepaksuste omavahelist erinevust, mis osutus kohati pea 3-kordseks, on alust arvata, et CHBDC meetod annab kahtlaselt väikesed terasepaksuste tulemused. Eeltoodut arvesse võttes on töö autor arvamusel, et Eesti tingimustes on terastorusildade kandevõimearvutuste teostamisel sobilikuks meetodiks SDM. Kuna SDM 63 arvutusmeetodit on juba üle 30 aasta täismõõdus katsetustega eksperimentaalselt uuritud, siis võib seda meetodit lugeda piisavalt usaldusväärseks. Kui projekteerija siiski otsustab kasutada kandevõimearvutuste teostamisel CHBDC meetodit, tuleks rajatise ohutuses veendumiseks projekteerimise käigus teostada CHBDC meetodile paraleelsed kandevõimearvutused lõplike elementide meetodil. Arvutustulemustest järeldub, et kandevõime suurendamiseks on mõistlik terasepaksuse suurendamise asemel kasutada kõrgema tugevusklassiga terast, mida siiani ei ole Eestis väga laialdaselt praktiseeritud.

Soil steel composite bridge is a type of bridge where corrugated structural steel plates in combination with surrounding soil form a structure that is able to carry load. These kind of bridges have found widespread usage in Estonia in the last decade. As the market demands structures with bigger spans and smaller cover depth on top of the structures, the soil steel bridge industry moves fast towards delivering new solutions that offer the possibility to cover spans over 20 m. This causes a situation where the design of such structures in Estonia is not clearly regulated and there is a lack of understanding for design requirements of such structures. Authorities are aware of this situation and are continuously improving this area by regulating the design, construction and maintenance of such structures. At the time of writing this thesis, TTK University of Applied Sciences is developing a manual on design, construction and maintenance of soil steel structures, which should be published in June 2016. The aim of this thesis is to introduce and compare two calculation methods of soil steel composite bridges and suggest a suitable calculation method for Estonian conditions. One of these is a method developed in Sweden known as the Swedish Design Method (SDM), the other method is developed in Canada and can be found in the Canadian standard S6-14 Canadian Highway Bridge Design Code (CHBDC). To reach the aim of the thesis, the author chose three different closed shape pipe arch soil steel bridges with structural steel plate dimensions of 200 × 55 mm (also known as MultiPlate MP200), and made static calculations according to the SDM and CHBDC methods. Afterwards the comparison of the results was carried out. The static calculations were made with identical soil properties, cover depths and live load models. Calculations were made with variable cover depths in the range of 0,5 to 3,0 m with a step of 0,5 m. The live load models LM1, LM2 and LM3 (3600/200) used in the calculations were applied according to the standard EVS-EN 1991-2:2004+NA2007. The smallest required steel thickness for each of the structures was chosen based on the most severe load case for different cover depths. For the general calculations steel grade S235 was used. The results were later compared to the results of steel grade S355 (for S355 only the results of steel thickness are presented in the thesis). The results from SDM method showed that the most severe load model for all three profiles, with cover of depth from 1,0 to 3,0, was LM1. For cover 0,5 m, the severe load turned out to be LM2, also the results showed that LM3 influence rises with the increase of cover on top of the structure, which is caused by the number of axles of LM3, which have more influence on the soil steel bridge with bigger cover depth and wider span. The results from CHBDC showed that the most severe load model in every case is LM1. This is caused by the principal of how concentrated loads are spread through the soil fill in the CHBDC method, which in the author’s opinion is not conservative. The calculations reveal, that in the CHBDC there is a specific load model (CL-W truck) predefined in the method for static calculations, which is different from the load models defined in Eurocode. As in Estonia the load models from the Eurocode are mandatory in static calculations, there is a need to combine the CHBDC method with Eurocode load models, which may be in conflict with the CHBDC concept of calculating the arising internal forces from the live load in the walls of the structure. Based on this, the CHBDC should not be used in Estonia as long as there are no additional comparative analyses made between the two methods (SDM and CHBDC). When comparing the smallest steel thickness from SDM and CHBDC, which differs almost up to 3 times, it is evident that CHBDC gives too optimistic results regarding the required steel thickness. Taking into account that Swedish Design Method was first presented in year 2000 and constantly developed by investigations calibrated by several full scale tests, and by the time of writing this thesis, presented in its 5th edition, it can be concluded that this method is sufficiently reliable. Based on previously given information, the author of this thesis suggests that the Swedish Design Method is the most suitable method for making static calculations for soil steel composite bridges in Estonian conditions. Secondary conclusion based on the calculation results is that in comparison of the required steel thickness and the cost of material unit price between the two different steel grades, it is evident that the amount of saving from using higher steel grade (S355 instead of S235) and smaller thickness, is appreciably more cost-efficient than using steel grade S235 with bigger thickness.