A Model to Determine the Contractors’ Claims of Construction projects

Complexity, dynamicity and uniqueness of construction projects, in addition to high financial turnover and numerous human resources increase the possibility and potential of claim between involved parties of execution. So claim is common involved and possible matter of subject. As the financial, qualitative and time effects of claims are high, it is necessary to recognize the contractors’ claim accurately in order to take an appropriate decision. In this study, a new model is presented to recognize the contractors’ claim which included three parts: common frequent claims, causes, and origins. To codify and design the model, 140 common claims and 60 causes which are originated of 7 origins were recognized. The model is used as decisive, determining, and anticipating model

A Model to Determine the Contractors’ Claims of Construction projects

Complexity, dynamicity and uniqueness of construction projects, in addition to high financial turnover and numerous human resources increase the possibility and potential of claim between involved parties of execution. So claim is common involved and possible matter of subject. As the financial, qualitative and time effects of claims are high, it is necessary to recognize the contractors’ claim accurately in order to take an appropriate decision. In this study, a new model is presented to recognize the contractors’ claim which included three parts: common frequent claims, causes, and origins. To codify and design the model, 140 common claims and 60 causes which are originated of 7 origins were recognized. The model is used as decisive, determining, and anticipating model

Finite Element Analysis on Reinforced Concrete Columns Strengthened by ECC Jacketing under Eccentric Compressive Load

Engineered cementitious composite (ECC) can be used for strengthening of concrete columns due to its similar structure and suitable connection to normal concrete and its special tension behavior. In this study, to analyse the columns, finite element (FE) method was used after verification by experimental results. Reference column was strengthened by normal concrete and ECC jacketing. The effects of type of jacket material, longitudinal reinforcement, compressive stress and ultimate tensile strain of ECC on variations of eccentric load-bending moment (P-M) interaction curves were investigated. Results showed that the use of ECC instead of normal concrete can increase load carrying capacity of strengthened column, due to tensile strain hardening behavior of this material. It was found that, amount of this increase depends on eccentricity of eccentric load and varying from 0.4-23%. In ECC jacketing, tensile cracks are continuous, but in concrete jacketing, there were discrete cracks and more quantity of damages. Due to higher load carrying capacity and better distribution of tensile cracks in ECC jacketing than normal concrete jacketing, the use of ECC is suitable for strengthening of reinforced concrete columns. Load carrying capacity of columns under concentric load and pure bending moment were calculated by theoretical method and the results were compared with FE

Static and Dynamic Analysis of Cracked Concrete Beams Using Experimental Study and Finite Element Analysis

In this paper, a simple method for defining the effects of cracks on elastic behavior of beam is presented. The cracked sections were modelled as rotational springs and the problem was solved using the finite element method. The global stiffness matrix of a beam with multiply cracked section was then assembled. For calculation of rotational spring stiffness equivalent to uncracked and cracked sections, finite element models and experimental test were used.The natural frequencies and mode shape of beams with multiple single-edge cracks were obtained and a new simple formula was proposed. Published numerical examples for cracked beams were used for validation

Behavior of large-scale bracing system in tall buildings subjected to earthquake loads

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 the lateral displacement, drift ratio, uplift forces in foundation and increases the ductility and shear absorption percent of the bracing system. Moreover, the stress ratios in the structural members of LSB system are less than the relevant values in other bracing systems

Seismic Performance of High-Rise RC Shear Wall Buildings Subjected to Ground Motions with Various Frequency Contents

Construction of tall buildings in societies is rising up for the increased population and limitation in horizontal expansion of cities. Therefore, behavior of these structures against earthquake essentially requires investigation. Recent research has shown that frequency content parameter of an earthquake has remarkable impacts on seismic response of buildings. This study aimed to investigate direct effects of frequency content on high – rise buildings. Thus, six Reinforced Concrete (RC) central core 10, 15, 20, 25, 30, and 35- story buildings were built in open source software OpenSees, and their seismic behavior under seismic records with various frequency contents were investigated. In this research,  non – linear dynamic Time – History was carried out and also behavior of buildings was compared in drift, shear force of stories, and maximum displacement of stories. Results of Time – History analysis showed that low – frequency content records have the highest effects on buildings. Most of the responses of drift and displacement of stories pertained to low – frequency contents in low – rise 10 and 15-story buildings. Although the most shear force of stories was related to low – frequency contents, with increasing height of buildings, shear force of stories increased, too. So that under Kobe Japan record which has the lowest frequency content among all records in this paper. Maximum shear force of stories was 6840 ton in 10-story building, whereas it was 12332 ton in 35- story building

Strengthening of Vulnerable RC Moment Resisting Frames Using Direct Internal Connection of X-Steel Bracing

Non-ductile reinforced concrete frames are commonly found in older buildings in many parts of the world. These structures are designed for gravity loads, have limited lateral strength and ductility, are prone to excessive one-way lateral movement and soft-story mechanism. This paper focuses on the retrofit of an existing reinforced concrete frame, using steel X-braces by direct internal connection method. The main purpose is the analytical study of general behavior and response of large-scale vulnerable frames. An experimental study was used to validate the numerical modelling performed in ABAQUS. Next, the base models were retrofitted with X-braces and four proposed direct internal connection methods. Additionally, in separate parametric studies, the effect of frame-type, bracing cross-section dimensions and gusset plate shape were investigated. The results indicated that the stiffness, bearing capacity and absorbed energy of the reinforced concrete frame by using steel X-braces increases up to 4, 2.3 and 1.5 times, respectively. Moreover, bracing acts like the first defense system against lateral loads, such as structural fuse with its yield, increases the amount of energy dissipation. It also removes the plastic hinges by reducing the ultimate displacement and stress of lateral load in the panel zone

Experimental Investigation of Connection Details on the Cyclic Performance of All-steel Tubular Buckling Restrained Braces

To eliminate the geometrical defects and to reduce the damage caused by out-off-plane rotation of the end portion of the conven-tional buckling restrained braces, as well as introducing a new way to facilitate the construction and installation process, the exper-imental behavior of 5 proposed specimens as new type of all-steel tubular buckling restrained braces (AST-BRB) under cyclic axial loads was studied.The proposed specimens consist of a steel tube as a load bearing member (core), which is placed inside a larger tube as a buckling restraining member (pod). At the two ends of the core member, different end details and connection (compared to the common BRBs) are provided as the elastic transitional region. The performance of the specimens were evaluated based on indices, such as damage mode, repeatable behavior, adjusted strength factors, load-bearing capacity, and cumulative inelastic displacement.The evaluation of the results indicated that, the specimens, which welded variable cross-section steel lids at both ends of the core, have superior seismic performance. The superior specimens, for all cycles with larger displacements of the yielding displacement, exhibited a stable hysteresis behavior in bearing of cyclic loads. The bearing pressure was about 1.07 times greater than the tensile load. The cumulative inelastic axial displacements of these specimens is at least 209 times of their yield displacement. Meanwhile, they can tolerate at least 140 % compressive load and 10 % greater tension loads relative to the nominal capacity of the core individual

The Resistance of Fiber-reinforced Concrete with Steel Fibers and CFRP to Drop-weight Impact

In this paper, the effects of macro-synthetic steel fibers and bidirectional carbon fiber-reinforced polymers (CFRPs) on the impact resistance of concrete specimens were studied. 54 concrete cylindrical specimens with different compressive strengths (20, 30, and 40 MPa) and with different fiber content ratios (0 %, 1 %, 1.5 %, and 2 %) were tested under impact loading. Half of these specimens were tested with the CFRP wrapping. The specimens were subjected to weight (46.7 and 66.8 kg) dropping at a height of 1.62 m. The process of weight dropping was continued until 30 % weight loss in the specimens was observed and the number of weight droppings related to this loss was recorded. Results indicated that the impact resistance of the concrete specimens (corresponding to the number of weight droppings) increased by using steel fibers or CFRP wrapping, separately. However, the results demonstrated that the specimens wrapped with the CFRP sheets had much further impact resistance than the FRCs without wrapping. Finally, the results showed that the greater the compressive strengths of the concrete, the better the impact resistance

Prediction models for bond strength of steel reinforcement with consideration of corrosion

Corrosion phenomena is one of the main deterioration causes, which remarkably affects the behavior of structural reinforced concrete (RC) members in seismic regions. Researches on reducing rehabilitation cost, performance assessment, and accurate modelling of corrosion-affected RC structures are progressively becoming popular in recent years. Corrosion diminishes bond capacity between reinforcement and surrounding concrete, which induces reduction in strength and ductility of members. The aim of this investigation is to provide a prediction approach based on a large number of results from published researches related to corroded reinforcement in concrete members using artificial neural networks (ANN). The minimizing mean square error criterion and increasing regression value of predicted results are considered for evaluation of training performance of ANN models. The validity of proposed model is checked using collected experimental database. Results show that estimated model has acceptable agreement with experimented data.publishedVersio