Fiber Beam Analysis of Reinforced Concrete Members with Cyclic Constitutive and Material Laws

This paper presents a non-linear Timoshenko beam element with axial, bending, and shear force interaction for nonlinear analysis of reinforced concrete structures. The structural material tangent stiffness matrix, which relates the increments of load to corresponding increments of displacement, is properly formulated. Appropriate simplified cyclic uniaxial constitutive laws are developed for cracked concrete in compression and tension. The model also includes the softening effect of the concrete due to lateral tensile strain. To establish the validity of the proposed model, correlation studies with experimentally-tested concrete specimens have been conducted

Practical computational toolkits for dendrimers and dendrons structure design

Dendrimers and dendrons offer an excellent platform for developing novel drug delivery systems and medicines. The rational design and further development of these repetitively branched systems are restricted by difficulties in scalable synthesis and structural determination, which can be overcome by judicious use of molecular modelling and molecular simulations. A major difficulty to utilise in silico studies to design dendrimers lies in the laborious generation of their structures. Current modelling tools utilise automated assembly of simpler dendrimers or the inefficient manual assembly of monomer precursors to generate more complicated dendrimer structures. Herein we describe two novel graphical user interface (GUI) toolkits written in Python that provide an improved degree of automation for rapid assembly of dendrimers and generation of their 2D and 3D structures. Our first toolkit uses the RDkit library, SMILES nomenclature of monomers and SMARTS reaction nomenclature to generate SMILES and mol files of dendrimers without 3D coordinates. These files are used for simple graphical representations and storing their structures in databases. The second toolkit assembles complex topology dendrimers from monomers to construct 3D dendrimer structures to be used as starting points for simulation using existing and widely available software and force fields. Both tools were validated for ease-of-use to prototype dendrimer structure and the second toolkit was especially relevant for dendrimers of high complexity and size.Peer reviewe

Evaluation of code criteria for bridges with unequal pier heights

One of the challenges associated with Eurocode 8 and AASHTO-LRFD is predicting the failure of irregular bridges supported by piers of unequal heights. EC8 currently uses “moment demand-to-moment capacity” ratios to somewhat guarantee simultaneous failure of piers on bridges, while AASHTO-LRFD relies on the relative effective stiffness of the piers. These conditions are not entirely valid, in particular for piers with a relative height of 0.5 or less, where a possible combination of flexure and shear failure mode may occur. In this case, the shorter piers often result in brittle shear failure, while the longer piers are most likely to fail due to flexure, creating a combination of different failure modes experienced by the bridge. To evaluate the adequacy of EC8 design procedures for regular seismic behavior, various irregular bridges are simulated through a non-linear pushover analysis using shear-critical fiber-based beam-column elements. The paper investigates the behavior of irregular monolithic and bearing-type bridges experiencing different failure modes, and proposes different methods for regularizing the bridge performance to balance damage. The ultimate aim is to obtain a simultaneous or near-simultaneous failure of all piers irrespective of the different heights and failure mode experienced

Simulation of post-tensioned bridge columns under reversed-cyclic loads

Thin-walled prestressed concrete structures such as bridge columns can be subjected to large magnitudes of dynamic loads. It is essential to develop a robust model to accurately predict the nonlinear behavior of these structures and thereby ensure their structural integrity under extreme loading conditions. A research project was performed to study the properties of prestressed concrete (PC) elements under shear loads using the Universal Panel Tester built at the Structural Engineering Lab of University of Houston. The test results were used to develop the softened membrane model for prestressed concrete (SMM-PC) (Wang, Constitutive relationships of prestressed concrete membrane elements, 2006). SMM-PC has been extended to the cyclic softened membrane model for prestressed concrete (CSMM-PC) by using the cyclic softened membrane model (CSSM) for reinforced concrete (Mansour and Hsu, J Struct Eng 131:44-53, 2005, J Struct Eng 131:54-65, 2005) CSMM-PC has been implemented into a finite element program to simulate the non-linear behavior of PC structures under cyclic loads. The program thus developed was named simulation of concrete structures (SCS). SMM-PC has been previously validated by tests on prestressed concrete beams under monotonic loading (Laskar et al., 12th international conference on engineering, science, construction, and operations in challenging environment, earth and space, 2010). In this paper CSMM-PC incorporated in SCS has been validated by tests on precast post-tensioned axisymmetric bridge columns under reversed cyclic loading. The analysis results of the bridge columns using SCS showed good agreement with the test results in terms of the primary backbone curves and the hysteretic loops including the energy dissipation and the strength degradation in the post-peak region. The damage and residual drift of the specimens were also closely predicted from the analysis results. Based on the accuracy of the analytical results it can be concluded that CSMM-PC implemented in SCS is an effective tool to simulate the cyclic non-linear behavior of thin-walled pre-stressed concrete structures and can be used for simulation of 3D actions of these type of structures through proper implementation

A Group of Hermits and the Patern of Their Seclusive Lives in the Tang Dynasty

Codes specify high factory of safety in design to prevent brittle torsional failure of reinforced concrete (RC) columns. This necessitates accurate prediction of the torsional behavior for efficient design of these members. However, very few analytical models are available to predict the response of RC members under torsional load condition. Softened truss model (STM) developed in the University of Houston is one of them, which is widely used for this purpose. The present study shows that STM prediction is not sufficiently accurate particularly in the post cracking region when compared to test results. It also aims at developing an improved analytical model for RC square members under torsional load conditions. Since concrete is weak in tension, its contribution to torsional capacity of RC members was neglected in the original STM. The present investigation revealed that, disregard to tensile strength of concrete is the main reason behind the discrepancies in the STM predictions. The original STM has been extended in this study to include the effect of tension stiffening (TS) to get an improved prediction of torsional behaviour of RC members. Three different tension stiffening models have been considered in this paper. The efficiencies of the models were calibrated through comparison with test data on local and global behaviours. The exponential tension stiffening model is found to give more accurate predictions