Ali Kheyroddin

Plastic Hinge Rotation Capacity of Reinforced HPFRCC Beams

High performance fiber reinforced cementitious composite (HPFRCC) materials exhibit strain hardening behavior under tensile loading. This strain hardening response occurs after the first cracking of the material. In this paper, experimental and parametric studies were conducted to assess the influence of the compressive strength, loading type, and tension reinforcement ratio (ρ) on the ultimate deformation characteristics of reinforced HPFRCC beams. The analytical and numerical results for simply supported beams with different amounts of tension reinforcement ratios under three different loading conditions are presented and compared with each other and with the available experimental data. The plastic hinge rotation capacity increases as the loading condition changes from the concentrated load in the middle to the uniform load, and it reaches a maximum in the case of two-point loading. The effect of loading type on the plastic hinge rotation capacity of the reinforced beams with a high amount of ρ is not as significant as that of lightly reinforced beams. Based on the analytical results, new simple equations as a function of the tension reinforcement ratio and the loading type are proposed. Analytical results indicate that the proposed equations can be used with sufficient accuracy to calculate the plastic hinge rotation capacity of reinforced HPFRCC beams.

A new method for damage prognosis based on incomplete modal data via an evolutionary algorithm

In this study, a new method is proposed to provide the location and the extent of structural damage by using incomplete modal data and an evolutionary algorithm. The proposed method uses modal data to formulate objective function. This data is acquired by the modal analysis of damaged structure applying the finite element method. The particle swarm evolutionary algorithm is employed to detect damage in structural elements by optimising an objective function. Three illustrative test examples with noise (noise 5 and 8%) and without noise in modal data were considered to evaluate performance of the proposed method. Moreover, the experimental data from the vibration test of a mass-stiffness system were used for verification of the proposed method. The obtained results indicated that this method can provide a reliable tool to accurately identify the structural damage.

Dominant pulse simulation of near fault ground motions

In this study, a new mathematical model is developed composed of two parts, including harmonic and polynomial expressions for simulating the dominant velocity pulse of near fault ground motions. Based on a proposed velocity function, the corresponding expressions for the ground acceleration and displacement time histories are also derived. The proposed model is then fitted using some selected pulse-like near fault ground motions in the Next Generation Attenuation (NGA) project library. The new model is not only simple in form but also simulates the long-period portion of actual velocity near fault records with a high level of precision. It is shown that the proposed model-based elastic response spectra are compatible with the near fault records in the neighborhood of the prevailing frequency of the pulse. The results indicate that the proposed model adequately simulates the components of the time histories. Finally, the energy of the proposed pulse was compared with the energy of the actual record to confirm the compatibility.

A two-stage method for structural damage prognosis in shear frames based on story displacement index and modal residual force

A two-stage method is proposed to properly identify the location and the extent of damage in shear frames. In the first stage, a story displacement index (SDI) is presented to precisely locate the damage in the shear frame which is calculated using the modal analysis information of the damaged structure. In the second stage, by defining a new objective function, the extent of the actual damage is determined via an imperialist competitive algorithm. The performance of the proposed method is demonstrated by implementing the technique to three examples containing five-, ten-, and twenty-five-story shear frames with noises and without them in modal data. Moreover, the performance of the proposed method has been verified through using a benchmark problem. Numerical results show the high efficiency of the proposed method for accurately identifying the location and the extent of structural damage in shear frames.

BEHAVIOR OF LARGE-SCALE BRACING SYSTEM IN TALL BUILDINGS SUBJECTED TO EARTHQUAKE LOADS

Abstract Bracing is a highly efficient and economical method of resisting of lateral forces in a steel structure. The most common types of bracing are those that form a fully triangulated vertical truss. These include the concentric and eccentric braced types. In high-rise buildings, the location and number of bracings is an important limitation to the architectural plan. A similar scheme has been used in larger scale spanning multiple stories and bays in tall buildings which is called large-scale bracing system. Large-scale bracing (LSB) is a particular form of a space truss. It consists of multiple diagonal elements that form a diagonal grid on the face of the structure. In this paper, a 20 story steel frame with different arrangement of bracing systems is analyzed. Linear and static nonlinear (push-over) analyses are carried out and the results presented here. Analytical results show that, the large-scale bracing is more adequate system under the lateral loads. Using LSB in tall buildings, decreases th...

Behavior of partially encased composite members under various load conditions: Experimental and analytical models

This study addresses the experimental behavior of octagonal partially encased composite column under axial and bending load conditions. The complementary study on axial and combined axial–torsional behavior is done through finite element analysis. The main parameters for the experiment part are reinforcement details and failure modes. The six parameters of this analytical analysis include width-to-thickness ratio of flange, transverse links spacing and diameter, welding line arrangements, and different types of retrofit of cross-shaped steel (concrete encasement, use of stiffener plates and transverse links). To verify accuracy of the proposed three-dimensional finite element model, the axial behavior of the numerical models was compared with test specimens. Experimental results of the axial study show that concrete crushing phenomena and local buckling behavior occurred for all specimens under ultimate stage of loading. It should be noted that local buckling behavior occurred after crushing phenomena. The analysis of bending assessment demonstrated that the use of stirrups has no remarkable effect on increasing the effective bending moment strength of octagonal partially encased composite columns. Meanwhile, an equation was developed based on comprehensive parametric study of octagonal partially encased composite column using detailed finite element analyses. Under axial–torsional load conditions, one could conclude that steel shear plates should be placed at the end zones of column to heighten torsional resistance of member. Meanwhile, transverse links were found to exert marginal effect on torsional behavior of octagonal partially encased composite column.

Performance of Two-way RC slabs Retrofitted by Different Configurations of High Performance Fibre Reinforced Cementitous Composite Strips

A total of five two-way slabs were made and tested to failure. Three slabs were retrofitted with a variety of different types of retrofit configurations and two other slabs, having low and conventional reinforcement ratios, were used as control slabs. A novel technique of bonding, designated NSM-HPFRCC, is proposed. Flexural responses of all slabs are evaluated and the bonding behaviour and associated failure modes are investigated.