Farzad Hejazi

University of the West of England, Bristol | UWE Bristol · Faculty of Environment and Technology

Beam-column connection zones are high regions of interest in reinforced concrete (RC) structures, which are expected to respond elastically to seismic loads. Using carbon fiber-reinforced polymers (CFRP) to improve these connections, performance is critical in retrofitting deficient RC frames because existing slabs may pose numerous limitations in...

Coulomb friction is considered as a mechanical approach to diminish the structural responses during the excitations. However, in case of severe oscillations supplementary mechanisms are employed besides the friction to mitigate the destructive effects of the vibrations in structures. Therefore, the main goal of this research is to develop a new Hyb...

Recently, buckling-restrained braces (BRBs) have been widely implemented as seismic load resistance systems in buildings to enhance their response against dynamic vibration. However, during catastrophic earthquakes, the steel core in BRB devices fully yields, which causes the BRB to lose its functionality. While the incorporation of various filler...

In this study, an attempt has been made to develop a Fuzzy Logic Multi Verse Optimal Control (FLMVOC) system as a new adaptive real-time vibration control mechanism for structures subjected to seismic excitation and wind load by utilizing the capability of the stochastic optimization method and fuzzy logic technique. The magnetorheological damper (...

This paper presents a numerical and experimental assessment of a developed adjustable variable stiffness restrainer (AVSR) utilized for short span bridges. This restrainer has the ability to demonstrate multi stiffness capacity in different stages of bridge's superstructure movement to mitigate the severe damage of bridge due to an earthquake. The...

Within the last decades, the needed for communication towers has accelerated with the requirements for effective communication, especially for radio, radar, and television. The complexity configuration of the tower and limit access to the structure body especially inner part of the tower with hollow section is led the health monitoring of tower as...

Nowadays, various types of vibration damping systems are being implemented in different buildings to diminish seismic effects on structures. However, engineers are faced with the challenging task of developing an optimum design for structures utilizing a proper type of damping device based on new techniques such as the performance-based design meth...

Concrete is brittle and prone to cracking, especially under tensile forces. The gradual development and propagation of cracks would subsequently lead to brittle failure. The use of fibers is effective in restricting the propagation of cracks and improving the failure mode of cement composites. This study attempts to enhance the performance of Reinf...

This paper proposes a new multi-level spring restrainer (MLSR) that exhibits multi stiffness performance in different levels of movement of bridge superstructure to prevent unseating during applied dynamic loads. The analytical model of the proposed MLSR was formulated and the fabricated prototype was tested using dynamic actuator. Based on the dev...

One of the best techniques for isolating structures from the ground is the seismic isolation technique. Nowadays, square and circular base isolators are the most frequently employed shapes. Nevertheless, these configurations are not applicable for the wall-like structures; since the applied loads are not distributed in a way that provides a uniform...

One of the best techniques for isolating structures from the ground is the seismic isolation technique. Nowadays, square and circular base isolators are the most frequently employed shapes. Nevertheless, these configurations are not applicable for the wall-like structures; since the applied loads are not distributed in a way that provides a uniform...

The global market for tires is ever-growing, and partially replacing sand with crumb rubber (CR) as fine aggregates in concrete could reduce environmental pollution. However, the main barrier to the complete usage of recycled tire crumbs in construction is the deterioration effect of CR on the mechanical properties of cement-based composites. There...

Energy dissipation occurs through Coulomb friction and is considered a conventional type of mechanical damping mechanism in structures subjected to external loads. Structures that are subjected to severe dynamic excitations such as ground motion or wind are required to employ a supplementary dampening system in addition to the Coulomb damping to mi...

In this research, an Adjustable Bypass Fluid Damper (ABFD) is developed by utilizing a pair of external fluid flow pipes and flow control valves. The flow control valves control the flow pressure of the fluid passing through bypass pipes and adjusted the function of the fluid damper to limit the displacement of the structure within the allowable ra...

This study proposed a new scheme for the retrofitting of Reinforced Concrete (RC) beams using Carbon Fiber Reinforced (CFRP) rods restrained using steel plates and anchorage bolts called the mechanical anchorage system (MAS). This system also employed an external concrete jacket to cover the MAS and CFRP rods. The performance of the proposed techni...

The present framework proposed the development of a Hybrid Rubber‐Concrete Isolation Slab System (HRCISS) to support building structures subjected to horizontal and vertical vibration due to ground motion and machine or equipment operation in the structure. Given that the effect of the shape factor on both horizontal and vertical stiffness has yet...

In the present study, a new core-and-filler system was proposed to use in elastomer bearings as a substitution to hazardous lead core while improving the performance of base isolators. The proposed system utilizes steel core and filler consists of either granular or polymer materials in relation to this proposal, both pure sand and epoxy are used a...

Nuclear energy offers a wide range of applications, which include power generation, X-ray imaging, and non-destructive tests, in many economic sectors. However, such applications come with the risk of harmful radiation, thereby requiring shielding to prevent harmful effects on the surrounding environment and users. Concrete has long been used as pa...

Numerical modeling of tunnel-form buildings entails the utilization of 3D finite element models consisting of large numbers of shell and fiber elements. Accordingly, the non-linear analysis of such models under seismic excitations is both time consuming and computationally expensive, especially in the case of large scale structures. To address this...

Nowadays, fracture mechanics modeling for strengthening structural members is a challenging issue for structural engineers. The developed fracture mechanics modeling was applicable for identifying propagation of a crack in concrete structural members such as beam-column connections. In the present paper, a numerical model derived from nonlinear fra...

Previous studies about optimizing earthquake structural energy dissipation systems indicated that most existing techniques employ merely one or a few parameters as design variables in the optimization process, and thereby are only applicable only to simple, single, or multiple degree-of-freedom structures. The current approaches to optimization pro...

Abstract Recently, the partially prestressed concrete (PPC) has been widely used as an effective construction technique for structures to reduce yielding and damages. However, there is no proper analytical model for PPC frame elements (beam-column members) to perform the finite element analysis. Besides, an extensive review of the literature uncove...

Circular hollow reinforced concrete column will experience deterioration due to many causes such as natural disaster, corrosion, low quality and others. Therefore, structural strengthening is required since replacing the deteriorated column is costly. Carbon fibre reinforced polymer (CFRP) confinement is one of the common method used for column str...

Elastomeric bearing is the most common base isolation system for structures and bridges to dissipate effect of applied vibration and ground motion. To improve performance of the base isolators, lead core is implemented in the rubber bearings and it successfully enhances the damping and stiffness of elastomeric bearing. However, the most notable dis...

Recently, the partially prestressed concrete (PPC) has been widely used as an effective construction technique for structures to reduce yielding and damages. However, there is no proper analytical model for PPC frame elements (beam-column members) to perform the finite element analysis. Besides, an extensive review of the literature uncovered littl...

Nowadays, the demand for using jack-up platforms to carry out a large percentage of deep-water oil and gas exploration is steadily increasing. The response of jack-up platforms to the severe dynamic loads that may be encountered during the structure life is not examined enough. Therefore, this study attempts to investigate the response of jack-up p...

Nowadays by implementing of various machineries and equipment, the structures are subjected to multidirectional vibrations as combination of vertical and horizontal cyclic oscillations. The slabs are the main structural components, imposed to the dynamic loads due to vibrating generator machines and the load is transferring from slabs to the founda...

Correction to: Enhancing the Performance of Knee Beam–Column Joint Using Hybrid Fibers Reinforced Concrete

Dams were and still as one of the most reliable options to control flood, hydropower, water supply, and irrigation. However, most of the dams can fail due to geological, hydrological, and structural reasons. Two types of break are usually occurred either overtopping or piping depend on the dam structure and the amount of flood due to hydrological c...

The recent ground motion results indicated that the RC buildings are required to be retrofitted by different strengthening techniques. Nowadays, the external strengthening gain interest since its easy, cost effective and not required redesign of buildings. The CFRP sheets are suitable solution and utilized by a number of researchers. However, the n...

Recently, the bridge unseating prevention devices are widely used in active seismic zones. These devices are stiffness dependant, velocity dependant and energy dissipation devices. The energy dissipation devices are designed to overcome the energy that transfers from bridge substructure to superstructure. However, the current devices are not contro...

Many nations are already working toward full implementation of energy efficiency in buildings known as Green Building. In line with this perspective, this paper aims to develop a thermally efficient precast concrete sandwich panels (PCSP) for structural applications. Therefore, an experimental investigation was carried out to determine the thermal...

In the last 2 decades, application of viscous dampers as restrainer device (lock-up) in buildings and bridges to diminish harmful effect of vibrations. However, leakage issue in the viscous luck-up devices requires regular expensive maintenance procedure to prevent device performance failure and many researchers are encouraged to find an alternativ...

The use of fibers in cement composites has been shown to improve the mechanical properties of concrete through the fiber-bridging effect, which implies the fiber’s crack-resisting property. Additionally, the combination of two or more different fibers in the concrete mixture yielded better strength than the individual fibers due to its more versati...

The stability and safety of precast concrete structures furnished with different types of connections has been a focus of researchers and engineers in the recent decade. In this study, the new design for connection of precast walls has been proposed by implementing and installing a pair of U-shape steel channels to each wall as male and female part...

The tunnel-form building system as innovative construction industry is gaining popularity and progressing increasingly towards a more effective structural system due to minimizing expenses, human resources, and construction time. In the current paper, an attempt was launched to study the dynamic response of a 5-story tunnel-from structure subjected...

This paper reports the development of a numerical model for a nonlinear stiffness bracing (NCSB) system as a new lateral resisting technique for framed structures subjected to dynamic loading. The NCSB device is composed of two conical springs embedded into the device to limit the story drift through the attachment of cable bracings into the frame....

In analysis of different types of dams, i.e. arch, gravity, rockfill and Roller Compacted Concrete (RCC) dams, the effect of hydrodynamic water pressure as an effective factor must seriously be taken into consideration. In present study, the hydrodynamic effect is precisely deliberated in RCC dams and compared to hydrostatic pressure effect. For th...

Nowadays, tunnel-form building systems are frequently implemented in the construction of various buildings due to the quick construction process. The rubber base isolator is one of the most successful and practical techniques to enhance the performance of structures against lateral loads. Although the conventional isolators are available in circula...

The knee beam–column joint is a critical location in a Reinforced Concrete (RC) structure particularly when subjected to earthquake vibrations. The current structural design codes dictate the use of high amounts of steel reinforcements in the frame joint to manage large strain demands in seismic-prone regions. However, these codes could result in t...

Corrosion of steel reinforcement is a major concern particularly for the existing structurers surrounded by aggressive environment. Loss in the diameter of steel reinforcement bars occurs due to the corrosion of reinforced concrete element resulting in premature bar failure. Corrosion is also the main cause of the expansion of concrete sections whi...

Although the ductility energy ratio ( $$\mu_{E}$$ μ E ) of the reinforced concrete beam has been the topic of numerous study purposes and critical inquiry for the last decades, narrow consideration, especially in terms of reinforced concrete deep beams (RCDBs), is conducted to examine the ductility energy of hybrid-RC deep beams with various CFRP c...

The specific operating conditions in concrete box-type (tunnel-form) buildings would lead to the concentration of walls in the interior parts of the plan and lack of structural walls in the perimeter of the plan. In this situation, due to the considerable reduction in torsional stiffness, usually torsional vibration modes prevail over translational...

In this study, several simplified constitutive models and a damage plasticity model for ultra-high performance fiber reinforced concrete(UHPFRC)material with micro and hooked ends steel fibers, Bekaert Dramix 5D steel fiber, and Forta-Ferro synthetic fiber had been developed. Later, these constitutive and damage plasticity models were applied as an...

The use of fibers in cementitious composites yields numerous benefits due to their fiber-bridging capabilities in resisting cracks. Therefore, this study aimed to improve the shear-resisting capabilities of conventional concrete through the hybridization of multiple synthetic fibers, specifically on reinforced concrete structures in seismic-prone r...

The autoregressive method is one of the simple methods for modal identification of the output-only systems. However, through the autoregressive method, for identifying n modes at least n sensors are required which is considered as the main challenging issue of this method. Also, in order to extract acceptable modal parameters using this method it i...

Hybridization of fibers in concrete yields a variety of applications due to its benefits compared to conventional concrete or concrete with single type-fiber. However, the Finite Element (FE) modeling of these new materials for numerical analyses are very challenging due to the lack of analytical data for these specific materials. Therefore, an att...

During the previous major seismic events, the unseating of the bridge superstructure was caused by large relative displacements which exceeded the bridge seat length. Therefore, this paper aims to introduce a multi-level unseating prevention device (MLUPD) to control deck movement. This device is capable of providing lateral resistance force with d...

Abstract This paper presents the experimental studies on the ultimate shear capacity (Vj,u) of typical joints used in ultra-high performance fibre reinforced concrete (UHPFRC) precast segmental bridge girder (PSBG). Twelve (12) pilot-scale shear key joints UHPFRC specimens (i.e. six (6) with dry keyed joints and six (6) with epoxied keyed joints) w...

The harmonic excitation or force vibration can be described by means of sine function or by means of cosine function.

A single degree of freedom (SDOF) system describes structural motion with only one degree of freedom. This simplifies the analysis procedure because it is a system with only one displacement coordinate. SDOF system is often used for approximation during the early engineering stage, rather than during the detailed engineering stage.

Structural engineering does not only deal with dynamic load induced by nature, such as wind, tide and ground motion. Machine operated with a certain pattern that can be described mathematically. Unlike the natural phenomena, properties of machine vibration are consistent and can be determined easily. Therefore, dynamic load induced by machine is a...

Under equilibrium, a structure subjected to dynamic load immediately develops reaction force from three components: mass, damping and stiffness.

A multi-degree of freedom (MDOF) system describes structural motion with multiple degrees of freedom.

The stiffness and strength of joints are the main factors in providing stability and ductility of a structure during dynamic load such as earthquake. In the high-humidity areas, the reinforcement is exposed to corrosion, which commonly occurs in the joints, due to the presence of micro-cracks in the joints, shrinkage or other concrete casting issue...

The demand for novel technology for manufacturing lightweight concrete has increased in the global construction industry. Therefore, studies that explore alternative lightweight concrete systems for structural applications are urgently needed. The objective of this study is to develop structural fibered foamed concrete by the addition of polypropyl...

This study reports the development of variable stiffness bracing (VSB) system as the lateral resisting element for RC-framed structures subjected to dynamic load. This device can enhance the lateral stability of structures against dynamic loading. The developed VSB device includes a nonlinear leaf spring, which provides variable stiffness character...

A core system for buildings has been recognized as an effective tool for managing the response of the building when an earthquake happens by decoupling the building structure from potentially damaging earthquake-induced forces. A challenging issue in this context is the application of the configuration of the core system. A review of recent studies...

Joints between precast segmental bridge girders (PSBGs) represent the locations of discontinuity through which compression and shear forces are transmitted. Therefore, knowledge of the joint behavior to accurately predict the response of PSBGs is essential. The aim of this research is to investigate the shear behavior, shear capacity, and shear-tra...

This book discusses the conceptual theory of structural dynamics, using simplified methods and clear, concise explanations. It illustrates all the hypotheses in a simple and effective way and describes in detail the derivation of all related formulations. Further, comprehensive step-by-step explanations combined with conceptual derivations, drawing...

Designing FRP plated RC beams using full-interaction moment-curvature analysis would often suggest that the RC structure is brittle with debonding often occurring prior to yielding of the reinforcement steel. For that reason, researchers have looked into a displacement-based approach that takes into account the member debonding mechanism. The force...

In the past few decades, many efforts have been carried out to investigate and improve the cyclic performance of the precast structure joints using high-strength steel bars and plates. However, the utilization of high-damping rubber (HDR) is mainly limited as the bearing pad below the structural components to dissipate the cyclic energy. Hence, a n...