Investigations Into The Resistance of Sin Girders Reinforced With Tensioned Diagonal Braces

S t r e s z c z e n i e W pracy pokazano sposób zwiększenia nośności dźwigarów o falistym środniku w drodze zwiększenia ich postaciowej nośności poprzez zastosowanie korzystnie rozciąganych krzyżulców. Zastosowano krzyżulce w strefach przypodporowych zwiększające postaciową nośność dźwigara. Środnik przenosi wówczas większe obciążenie poprzeczne stowarzyszone ze zginaniem. Badania doświadczalne zwiększonej nośności postaciowej środnika dźwigarów przeprowadzono na dźwigarach o wysokości środnika 500, 1000 i 1500 mm. Oszacowano rozdział siły poprzecznej na falisty środnik oraz krzyżulce. Wyznaczono ścieżki postaciowej równowagi statycznej falistego środnika oraz krzyżulców. Wyniki badań nośności dźwigarów wzmocnionych krzyżulcami rozciąganymi porównano z badaniami dźwigarów bez wzmocnienia i z wynikami obliczeń wg Eurokodu 3. Artykuł stanowi pierwszą część opracowania. Sformułowano wnioski i zalecenia (w drugiej części opracowania) do wymiarowania dźwigarów o falistych środnikach, wzmocnionych krzyżulcami rozciąganymi. W drugiej części zostanie pokazane zastosowanie analizy numerycznej MES do teoretycznego oszacowania postaciowej i giętnej nośności granicznej oraz krytycznej dźwigarów o falistym środniku wzmocnionych krzyżulcami rozciąganymi. K e y w o r d s : Girders with corrugated web; Tension diagonal braces; Ultimate resistance; Critical resistance. 1/2017 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 53 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 1/2017 W . B a s i ń s k i , Z . K o w a l Experimental and theoretical investigations on the resistance of girders with thin-walled corrugated webs were carried out by many authors [1, 2, 3, 4, 5, 6, 7, 8, 9, 12, 13, 14, and 16]. In such girders, phenomena not found in conventional plate girders are still discovered. It often happens that the resistance of SIN girders designed in accordance with [18] is limited by the shear resistance of the web, and not by pure bending resistance. In many cases, the shear resistance of the girders with corrugated web is considerably lower than that under shear load associated with bending. According to the code [19], the resistance of flanges is calculated for pure bending load. In studies [2, 3, 4], it was shown that in SIN girders, two ultimate resistances are found, namely shear and flexural ones. The global flexural resistance of girders with corrugated web is most frequently limited by the shear resistance measured by shear forces that accompany bending, and the potential capacity of girder flanges is often not fully utilised. The present study shows the way of adjusting the shear resistance of the web to the associated flexural resistance of SIN girders by means of reinforcing the corrugated web, especially in the near-support zones. Diagonal braces, subjected to advantageous tension, carry considerably higher loads produced by shear forces. That is of particular importance because in the Eurocode [20], differences in the reliability of SIN girders loaded with pure bending and that of girders loaded with bending and associated shear forces were not accounted for. The application of diagonal braces is particularly useful when it is necessary to upgrade the existing structures made from corrugated web girders [11, 15] designed in accordance with European structural code and recommendations [19, 20]. That also refers to cantilever beams and beams with openings (Fig. 1). Investigations on shear resistance of girders with corrugated web, reinforced with tension diagonal braces located in the near-support zone, were performed using models shown in Fig. 2. Diagonal braces, subjected to advantageous tension as diagonal stiffeners, located on both sides, were used in the near-support zones of simply supported beams (Fig. 3). That means, in the sections, in which girder loading with shear force is greater than design shear resistance of the web. Diagonal braces were joined by welds, forming nodes together with vertical stiffeners and flanges (Fig. 3). 54 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 1/2017 Figure 2. Corrugated web girders, from which the models were made Figure 1. Girders with corrugated web: a) cantilever beam, b) beam with openings a b INVEST IGAT IONS INTO THE RESISTANCE OF SIN GIRDERS RE INFORCED WITH TENSIONED DIAGONAL BRACES Analytic calculations based on Eurocode 3 [20] were performed for the sake of making comparison with the results of tests. 2. GIRDERS SUBJECTED TO DESTRUCTIVE TESTING Items of SIN girders (Fig. 2) with the span of L = 3150 mm, web height of 500, 1000 and 1500 mm, made at 1:1 scale, were selected for testing. The elements were constructed in accordance with standards and recommendations [19, 20] from components shown in Fig. 2. Models of girders reinforced with tension diagonal braces made of S275 steel are presented in Fig. 3. The models were denoted as R 21 (WTA 500/300x15), R 22 (WTA 1000/300x15) and R 23 (WTA 1500/300x15). Corrugated webs, t = 2 mm in thickness, of the girders R 21, R 22 and R 23 were made of S235 steel, C I V I L E N G I N E E R I N G e 1/2017 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 55 Figure 3. Girders: a) R 21; c) R 22, f) R 23; b); d) girder and stiffeners; e) detail of welds g) view of the tested girders c