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Composite wood-concrete beams using utility poles / Richard M. Gutkowski in Journal of structural engineering, Vol. 137 N° 6 (Juin 2011) 

Public ISBD [article]  in Journal of structural engineering > Vol. 137 N° 6 (Juin 2011) . - pp. 625-634 Titre : Composite wood-concrete beams using utility poles : time-dependent behavior Type de document : texte imprimé Auteurs : Richard M. Gutkowski, Auteur ; Nathan J. Miller, Auteur ; Massimo Fragiacomo, Auteur Année de publication : 2011 Article en page(s) : pp. 625-634 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Composite  beams  Concrete  Connectors  Creep  Laboratory  tests  Notches  Poles  Wood  Time  dependence  Timber  construction Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper describes the behavior of wood-concrete composite beams in which the wood layer is composed of recycled utility poles. Two full-scale laboratory specimens of 7,500-mm (295-in.) span were constructed, with the concrete slab cast on the timber poles left unshored. The connection was obtained by cutting six notches in the timber poles. A threaded steel dowel is placed in each notch extending through both layers with a nut on the bottom of the beam that can be tightened once the concrete has cured. Since the material in each layer exhibits a time-dependent response, it is necessary to examine the effects of sustained loading. After 28 days of initial curing of the concrete layer during which the midspan deflection was monitored, both beams were subjected to the service load to estimate the composite efficiency. The beams were very stiff and values of 96% and 98% were obtained, respectively, demonstrating the high efficiency of the notched connection system used. A comparison was made with results obtained in the literature for ramp load tests of two similar specimens, which had exhibited composite efficiencies of about 94% and 96%, respectively. A sustained load of approximately 11% of the estimated static ultimate load capacity was then applied to one of the specimens, which was monitored over time. The applied load resulted in a midspan moment of 24  kN·m (212  kip·in.) while the calculated ultimate capacity corresponded to a midspan moment of 226.5  kN·m (2,005  kip·in.). The final deflection was found to increase to 44.4 mm (1.75 in.) after 256 days, which was more than twice the initial elastic deflection owing to the application of the dead and live loads. The deflection attributable to the dead load was 19.1 mm (0.75 in.), and the deflection attributable to the live load was 2.54 mm (0.10 in.). An existing one-dimensional (1D) finite-element program was utilized to predict the time-dependent deflection at the end of a 50-year service life. The comparison with experimental results showed good approximation, particularly for the midspan deflection. The software predicted a 54-mm (2.14-in.) midspan deflection at the end of a 50-year service life, corresponding to 1/139 of the span. This was sufficiently high to suggest that either larger cross-section and/or precambering of the wood layer could be needed when the serviceability limit state of maximum deflection in the long-term is a required performance criterion. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i6/p625_s1?isAuthorized=no [article] Composite wood-concrete beams using utility poles : time-dependent behavior [texte imprimé] / Richard M. Gutkowski, Auteur ; Nathan J. Miller, Auteur ; Massimo Fragiacomo, Auteur . - 2011 . - pp. 625-634. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 137 N° 6 (Juin 2011) . - pp. 625-634 Mots-clés : Composite  beams  Concrete  Connectors  Creep  Laboratory  tests  Notches  Poles  Wood  Time  dependence  Timber  construction Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper describes the behavior of wood-concrete composite beams in which the wood layer is composed of recycled utility poles. Two full-scale laboratory specimens of 7,500-mm (295-in.) span were constructed, with the concrete slab cast on the timber poles left unshored. The connection was obtained by cutting six notches in the timber poles. A threaded steel dowel is placed in each notch extending through both layers with a nut on the bottom of the beam that can be tightened once the concrete has cured. Since the material in each layer exhibits a time-dependent response, it is necessary to examine the effects of sustained loading. After 28 days of initial curing of the concrete layer during which the midspan deflection was monitored, both beams were subjected to the service load to estimate the composite efficiency. The beams were very stiff and values of 96% and 98% were obtained, respectively, demonstrating the high efficiency of the notched connection system used. A comparison was made with results obtained in the literature for ramp load tests of two similar specimens, which had exhibited composite efficiencies of about 94% and 96%, respectively. A sustained load of approximately 11% of the estimated static ultimate load capacity was then applied to one of the specimens, which was monitored over time. The applied load resulted in a midspan moment of 24  kN·m (212  kip·in.) while the calculated ultimate capacity corresponded to a midspan moment of 226.5  kN·m (2,005  kip·in.). The final deflection was found to increase to 44.4 mm (1.75 in.) after 256 days, which was more than twice the initial elastic deflection owing to the application of the dead and live loads. The deflection attributable to the dead load was 19.1 mm (0.75 in.), and the deflection attributable to the live load was 2.54 mm (0.10 in.). An existing one-dimensional (1D) finite-element program was utilized to predict the time-dependent deflection at the end of a 50-year service life. The comparison with experimental results showed good approximation, particularly for the midspan deflection. The software predicted a 54-mm (2.14-in.) midspan deflection at the end of a 50-year service life, corresponding to 1/139 of the span. This was sufficiently high to suggest that either larger cross-section and/or precambering of the wood layer could be needed when the serviceability limit state of maximum deflection in the long-term is a required performance criterion. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i6/p625_s1?isAuthorized=no