Efficient single-step time-dependent analysis of PC structures

This paper describes an efficient single-step method to predict the time-dependent behaviour of prestressed concrete (PC) structures due to concrete creep, concrete shrinkage and cable relaxation. A versatile tendon sub-element is first developed to model prestressing cables of arbitrary profiles. To enable accurate estimation of losses of cable forces, a new relaxation model is formulated based on the equivalent creep coefficient, which is verified to work not only in the case of intrinsic relaxation but also under various boundary conditions. An efficient single-step finite-element method is then devised for time-dependent analysis of PC structures considering creep, shrinkage and relaxation based on the age-adjusted elasticity modulus, shrinkage-adjusted elasticity modulus and relaxation-adjusted elasticity modulus respectively. The effects of creep, shrinkage and relaxation on the long-term performance of PC structures are investigated. The numerical results obtained indicate not only the accuracy of the method but also the significance of considering the interaction among various time-varying factors.published_or_final_versio

Experimental and numerical investigation of post-tensioned concrete flat slabs in fire

Session 1A: Concrete Structures (I)Tests of four post-tensioned high-strength self-compacting concrete flat slab specimens have been conducted under fire condition. Tendon distributions including distributed-distributed and banded-distributed patterns as well as various loading ratios were considered. Two of the specimens with lower moisture contents demonstrated excellent fire resistance performance, while the others with relatively high moisture contents experienced severe concrete spalling. The test results obtained from the tests are presented and discussed with respect to temperature distributions, deflections, crack patterns and concrete spalling. Moreover, numerical modelling employing the package ABAQUS has been conducted to help interpret the test results in order to get better understanding of slabs in fire.postprin

Time-dependent analysis of concrete bridges with creep, shrinkage and cable relaxation

Reinforced Concrete Structures: CC.120This paper describes a single-step method to predict the time-dependent behaviour of concrete structures due to concrete creep, concrete shrinkage and cable relaxation. Firstly, a new relaxation model for steel tendons based on the equivalent relaxation function is proposed to enable the accurate estimation of the losses of cable forces. Based on this new model, a relaxation-adjusted elasticity modulus is developed to enable the prestress loss to be analyzed using a single step. Then a general method is established for single-step finite element analysis for time-dependent deformations of concrete bridges under the effects of concrete creep, concrete shrinkage and cable relaxation, using the age-adjusted elasticity modulus, shrinkage-adjusted elasticity modulus and relaxation-adjusted elasticity modulus respectively. In this proposed method, concrete members are modelled using beam elements, while tendons are modelled as truss elements with nodes connected to the beam axis by perpendicular rigid arms. Numerical examples are analyzed using both the time integration method and the proposed single-step method. The good agreement of results demonstrates the accuracy and efficiency of the proposed method. © Civil-Comp Press, 2009.link_to_OA_fulltextThe 12th International Conference on Civil, Structural and Environmental Engineering Computing & the 1st International Conference on Soft Computing Technology in Civil, Structural and Environmental Engineering, Funchal, Madeira, Portugal, 1-4 September 2009. In Conference Proceedings, 2009, p. 1-1