Effects of tensile softening on the cracking resistance of FRP reinforced concrete under thermal loads

Panedpojaman, Pattamad,Pothisiri, Thanyawat Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.4

Fiber reinforced polymer (FRP) bars have been widely used as reinforcement for concrete structures. However, under elevated temperatures, the difference between the transverse coefficients of thermal expansion of FRP rebars and concrete may cause the splitting cracks of the concrete cover. As a result, the bonding of FRP-reinforced concrete may not sustain its function to transfer load between the FRP rebar and the surrounding concrete. The current study investigates the cracking resistance of FRP reinforced concrete against the thermal expansion based on a mechanical model that accounts for the tensile softening behavior of concrete. To evaluate the efficacy of the proposed model, the critical temperature increments at which the splitting failure of the concrete cover occurs and the internal crack radii estimated are compared with the results obtained from the previous studies. Simplified equations for estimating the critical temperature increments and the minimum concrete cover required to prevent concrete splitting failure for a designated temperature increment are also derived for design purpose.

Effects of tensile softening on the cracking resistance of FRP reinforced concrete under thermal loads

Pattamad Panedpojaman,Thanyawat Pothisiri 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.4

Fiber reinforced polymer (FRP) bars have been widely used as reinforcement for concrete structures. However, under elevated temperatures, the difference between the transverse coefficients of thermal expansion of FRP rebars and concrete may cause the splitting cracks of the concrete cover. As a result, the bonding of FRP-reinforced concrete may not sustain its function to transfer load between the FRP rebar and the surrounding concrete. The current study investigates the cracking resistance of FRP reinforced concrete against the thermal expansion based on a mechanical model that accounts for the tensile softening behavior of concrete. To evaluate the efficacy of the proposed model, the critical temperature increments at which the splitting failure of the concrete cover occurs and the internal crack radii estimated are compared with the results obtained from the previous studies. Simplified equations for estimating the critical temperature increments and the minimum concrete cover required to prevent concrete splitting failure for a designated temperature increment are also derived for design purpose.

Finite Element Investigation on Deflection of Cellular Beams with Various Configurations

Pattamad Panedpojaman,Thaksin Thepchatri 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.3

The effect of the cellular beam configuration on the deflection has been investigated by using the three-dimensional finite element analysis of 408 cellular beams. Cross-section dimension, beam slenderness, opening size and opening spacing are found to affect the stiffness of the analytical load-deflection curve. The parametric study of the FE stiffness and normalized stiffness is conducted. The stress distribution of the finite element (FE) model reveals the strut stress in the web-post contributes to the increasing deflection in addition to the regular bending deflection. The deformation of the web-post and the relative movement between the upper and lower tee-sections due to strut stress is the main reason of the additional deflection in the cellular beams. The effect of the strut stress is found to be significant for the deflection of the short-span beams but less for the long-span beams. To convert the theoretical bending deflection to be the overall deflection, the calibrating coefficient function is established by using the empirical study. The function is formulated in terms of the slenderness, spacing and cross section ratio. The deflection prediction is useful to check serviceability condition for the design purpose.

Simplified equations for Vierendeel design calculations of composite beams with web openings

Pattamad Panedpojaman 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.27 No.4

Composite beams with web openings are vulnerable to Vierendeel bending failure. The available methods provide quite conservative estimates of Vierendeel bending resistance. An alternative design method to compute the resistance was proposed in this study, based on quadratic nonlinear interactions of normalized shear force, axial force and Vierendeel bending moment. The interactions of the top and bottom Tee section must satisfy mutual conditions to prevent the Vierendeel failure. The normalized shear force and Vierendeel bending moment of the composite part were used instead in the top Tee interaction. The top Tee axial force was computed based on force equilibrium. Based on a rigid-plastic model, the composite resistance is estimated using an effective slab width of the vertical shear resistance. On using the proposed method, nonlinear reductions due to shear loads and axial forces are not required, in contrast to prior methods. The proposed method was validated against experiments from literature. The method limitations and accuracy as well as the Vierendeel behavior were investigated by finite element simulations, with varied composite beam parameters. The proposed design loads are less conservative than earlier estimates and deviate less from the simulations.

Deflection of composite cellular beams

Hnin Wai Hlaing,Pattamad Panedpojaman 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.2

The deflection of composite (cellular) beams is important for serviceability purposes. However, the available methods to predict the deflection are inaccurate. This research aims to propose a method for predicting the deflection with improved accuracy. The proposed deflection consists of contributions from overall flexural behavior and Vierendeel bending. In addition to the slip action, a reduction factor for computing the effective moment of inertia is investigated and used to compute the flexural deflection. The Vierendeel deformation was determined based on shear deflection of a virtual cantilever beam. No local composite action is conservatively assumed in the cantilever beam. Over 700 three-dimensional finite element (FE) models were simulated to investigate the reduction factor and limitations of the proposed method. The FE model was validated against 13 experimental load-deflection curves from the literature. The proposed method is suitable for predicting the deflection of composite cellular beams having the spacing ratio 1.35 or higher and the span ratio higher than 5. For such cases, the deflection estimate is from 0.90 to 1.05 times the FE deflection. The web-post deformation and the global shear deflection affect the prediction accuracy. In comparison to other methods, the proposed method is more accurate in predicting the deflection.

Nonlinear Frame Element with Shear– Flexure Interaction for Seismic Analysis of Non-Ductile Reinforced Concrete Columns

Worathep Sae-Long,Suchart Limkatanyu,Woraphot Prachasaree,Suksun Horpibulsuk,Pattamad Panedpojaman 한국콘크리트학회 2019 International Journal of Concrete Structures and M Vol.13 No.5

This paper presents and emphasizes the essence of inclusion of shear response and shear–flexural interaction in the investigation of reinforced concrete (RC) columns characterized by light and inadequately (substandard) detailed transverse reinforcement. This column type commonly exists in old-constructed RC frame buildings before the regulation of modern seismic codes. A stiffness-based RC frame element with shear–flexure interaction is formulated within the framework of Timoshenko beam kinematics assumption. Linked displacement interpolation functions are employed to remedy the problematic shear-locking phenomenon. The axial and flexural actions are interacted via the fiber-section model while shear-strength deterioration with inelastic flexural deformations is accounted for within the framework of the UCSD shear-strength model. The numerical procedure for shear–flexure interaction is modified from the Mergos–Kappos procedure. The proposed element is simple, computationally efficient and able to describe several salient features of RC columns with substandard detailed transverse reinforcement, including gradual spread inelasticity, shear–flexure coupling effects, and shear-strength deterioration with increasing curvature ductility. Three correlation studies are conducted to examine the model accuracy and its capability to predict the rather complex responses of non-ductile RC columns. Comparison with conventional flexural frame element is also presented to emphasize the essence of inclusion of shear response and shear–flexure interaction.