A design model for punching shear of FRP-reinforced slab-column connections

The overall aim of this paper is to develop a unified design method for the punching shear resistance of slab-column connections irrespective of the type of internal reinforcement. In the first part of the paper a design model for the punching shear resistance of concrete slab-column connections reinforced with fibre-reinforced polymers (FRP) is proposed. This design model is based on the authors’ theoretical analysis for such slabs, which considers the physical behavior of the connections under load. The effects of the inherent linear brittle response, the lower elastic modulus and the different bond features, as compared to steel, of the FRP reinforcement are all accounted for in the present study. The proposed model does not incorporate any fitting factors to match the theory to the trend of the available FRP slab test results. The excellent agreement between the predicted and published test results should give confidence to engineers and designers in using FRP as a sound structural reinforcement for slab-column connections. It is then shown that the proposed design model for FRP slabs and the previous model of the authors for steel reinforced slabs are both identical in nature and structure, thus constituting a unified approach to design for punching shear in slabs. On the basis of the unified model comparison and correlation between an FRP slab and a reference steel reinforced slab, confirmed by the available test results, are presented. The unified model also enables the development of a more rational and reliable equivalent steel reinforcement ratio which can be applied to existing code equations for steel reinforced slabs to estimate the punching resistance of FRP-reinforced slabs

Failure criteria for composite slabs subject to extreme loading conditions

This paper is concerned with the ultimate behaviour of composite steel/concrete floor slabs under extreme loading situations, particularly those that occur during severe building fires. The study focuses on the failure state associated with rupture of the reinforcement in composite slab members which become lightly reinforced in a fire situation due to the early loss of the steel deck. An account of a series of large scale ambient tests, undertaken on full slab members, is presented in the paper. The experimental arrangements are described together with the details of the specimens. Complementary analytical studies, carried out to assess the salient factors influencing the failure of composite slab members are also summarised. The assessments utilise detailed numerical models which adopt novel finite element formulations including geometric and material nonlinearities, as well as simplified analytical models for the prediction of failure deformations and associated load levels. The results of this investigation offer detailed insights into the key factors that govern the ultimate behaviour of composite floor systems under extreme loading conditions, and provide simplified tools which are suitable for implementation in performance based design procedures

An Experimental Study of a Flat Slab Floor Reinforced with Welded Wire Fabric

Reinforced Concrete Reserach CouncilOffice of the Chief of Engineers, U.S. Army.General Services Administration, Public Buildings ServiceHeadquarters, U.S. Air Force. Contract AF 33(658)-47U.S. Navy, Engineering Division. Bureau of Yards and Docks. NBy 3763

Azobenzene versus 3,3',5,5'-tetra-tert-butyl-azobenzene (TBA) at Au(111): Characterizing the role of spacer groups

We present large-scale density-functional theory (DFT) calculations and temperature programmed desorption measurements to characterize the structural, energetic and vibrational properties of the functionalized molecular switch 3,3',5,5'-tetra-tert-butyl-azobenzene (TBA) adsorbed at Au(111). Particular emphasis is placed on exploring the accuracy of the semi-empirical dispersion correction approach to semi-local DFT (DFT-D) in accounting for the substantial van der Waals component in the surface chemical bond. In line with previous findings for benzene and pure azobenzene at coinage metal surfaces, DFT-D significantly overbinds the molecule, but seems to yield an accurate adsorption geometry as far as can be judged from the experimental data. Comparing the trans adsorption geometry of TBA and azobenzene at Au(111) reveals a remarkable insensitivity of the structural and vibrational properties of the -N=N- moiety. This questions the established view of the role of the bulky tert-butyl-spacer groups for the switching of TBA in terms of a mere geometric decoupling of the photochemically active diazo-bridge from the gold substrate.Comment: 9 pages including 6 figures; related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm

Failure assessment of lightly reinforced floor slabs. I: Experimental investigation

This paper is concerned with the ultimate behavior of lightly reinforced concrete floor slabs under extreme loading conditions. Particular emphasis is given to examining the failure conditions of idealized composite slabs which become lightly reinforced in a fire situation as a result of the early loss of the steel deck. An experimental study is described which focuses on the response of two-way spanning floor slabs with various materials and geometric configurations. The tests enable direct assessment of the influence of a number of key parameters such as the reinforcement type, properties, and ratio on the ultimate response. The results also permit the development of simplified expressions that capture the influence of salient factors such as bond characteristics and reinforcement properties for predicting the ductility of lightly reinforced floor slabs. The companion paper complements the experimental observations with detailed numerical assessments of the ultimate response and proposes analytical models that predict failure of slab members by either reinforcement fracture or compressive crushing of concrete. © 2011 American Society of Civil Engineers

Numerical modelling of symmetric and asymmetric punching and post-punching shear responses of RC flat slabs

The design and construction of civil engineering structures take into great consideration the sensitivity of such structures in the event of local failures. Flat slab structural systems are very prone to progressive collapse after the failure of a connection or column. Hence, to improve their robustness the introduction of integrity reinforcement is recommended in Eurocode 2, ACI 318-11 and Model Code 2010. However, very little investigation has been carried out on the asymmetric post-punching response of these connections or the actual contribution of designed integrity reinforcement to robustness at a system level. Presented in this paper, is a numeric approach developed for modelling the response of isolated RC flat slab test specimens using the finite element (FE) software LS-DYNA. This is in view of their incorporation into system models for both quasi-static and dynamic assessments of robustness in flat slab structures. Quarter FE models of four symmetric isolated RC flat slab specimens with experimental responses available in literature were developed. These quarter FE models were analysed numerically using a quasi-static displacement controlled approach and their flexural, punching shear and post-punching shear responses observed. A sensitivity analysis was carried out to obtain the optimum element characteristics for punching shear strength as well as other response criteria. Half asymmetric F.E models of two slab specimens were also developed and analysed. These provided the asymmetric punching and post-punching shear response of the slab specimens, assuming the loss of an interior column. Results of quarter symmetric FE models gave accurate predictions of slab load-deformation responses, punching and post-punching shear strengths. Maximum percentage differences of 2% and 3% were obtained when comparing test and FE results of symmetric slab specimens for peak punching and post-punching shear strengths respectively. Asymmetric FE models gave post-punching shear strengths lower than values obtained from tests on symmetric specimens. Robustness of flat slab structures after the loss of an internal column could be significantly overestimated where models adopted do not take into consideration such reductions in post punching shear strength. The results presented validate the use of this FE approach on LS-DYNA to predict the response of concrete flat slab connections

The Effects of Pattern Loadings on Reinforced Concrete Floor Slabs

Reinforced Concrete Reserach CouncilOffice of the Chief of Engineers, U.S. Army.General Services Administration, Public Buildings ServiceHeadquarters, U.S. Air Force, Directorate of Civil Engineering.U.S. Navy, Engineering Division. Bureau of Yards and Docks. NBy 3763

Diffraction of long period Rayleigh waves effects of mode coupling by a slab: effects of mode coupling

International audienceWe compute seismograms of the fundamental Rayleigh waves propagating through a slab structure , with either a lateral variation in seismic velocities , or in attenuation. At periods of 100 sec, we show that the phase delay is strongly reduced by the surface waves Fresnel zone, and that coupling must be considered far along the dispersion branch, up to at least oe-• 25. Limiting the coupling to fewer modes produces a signal associated to a ghost structure at the antipode of the slab. We also show that the amplitude perturbations produced by the diffraction and the attenuation of the slab are comparable in size. Future waveform studies, especially those associated to global waveform inversions, must then carefully consider these effects