Examination of Northridge fractured connections has revealed that the materials and the manufacturing parameters associated with the fracture behaviour of these connections are random. Hence, the fracture resistance and ductility of these connections are also random. In this study, most of the parameters which are believed to contribute to the fracture behaviour of Northridge connections are analysed with respect to previous research in the field. Then one of the pre-tested post-Northridge connections is modelled, using finite-element analysis and the results are used as typical examples to illustrate the effect of each parameter on the behaviour of these connections. Experimental fracture moment and ductility data of a set of previously conducted tests on the pre-and post-Northridge design are used to obtain suitable cumulative distribution functions of the normalised fracture moment and plastic rotation of these types of connections. Statistical results show that, despite all the modifications applied to the pre-Northridge connections, the magnitude of the minimum plastic rotation and the strength are still less than what is required by the seismic codes. Therefore, both pre- and post-Northridge connections do not have enough strength and ductility and consequently they are not reliable and should be further modified when used in seismic regions.
In addition to the positive effects of industrial development and technological progress, it also has adverse side effects such as increasing the quantity and quality of working and living environment pollution. Work-related accidents and occupational diseases are the consequences of the development of industry and technology and they increasingly threaten human life, especially the staff. Work-related Accidents are accidents that occur in the line of duty in the workplace and lead to fatal or non-fatal injuries. Although many activities have been done to reduce work-related, or in other words occupational accidents, the accident statistics is still high, in a way that The World Health Organization considered that as an epidemic in the area of public health, and considered that as a critical risk factor for health, economic and social issues. This paper deals with safety culture, costs arising from accidents and how to cope with the work-related accidents.
Due to the closed shape of box columns and difficult access to its inside for developing a reliable load path regarding rigid I-beam to box columns connections, in this study, some alternatives have been suggested to replace continuity plates. These alternatives are: two triangular plates, two rectangular plates and added stiff web. To evaluate the efficiency of these suggested alternatives, using ANSYS software, several beam-column connections in each alternative have been modeled. Based on the finite element results the behavior of Ibeam connection to steel box column has been studied. Then the effects of suggested stiffeners on connection stiffness, strength and ductility have been investigated. The results showed that each of the suggested methods might be a good alternative for rigid connection with internal uniform continuity plates. However specimens of additional stiffened webs achieved highest connection strength and ductility.
Background: Generally, in traumatic patients, uncontrolled bleeding leads to shock and ultimately death. So, any early detection of shock can reduce the likelihood of a patient’s death. At present, the precise method for estimating the body’s need for fluids is to measure central venous pressure (CVP). However, this method is invasive and time consuming. Objective: This study aimed to predict the central venous pressure value and range of trauma patients through non-invasive parameters such as caval index, lactate clearance, base excess and shock index. Methods: A prospective observational study was performed in 100 trauma patients. Written informed consent was obtained from patient(s) or relatives for their anonymized information to be published in any article. Results: It indicated that parameters such as caval index (at a proposed cutoff point of 35%), lactate clearance (at a cutoff point of 6%) and base excess (at a proposed cutoff point of 6 mmol/L) are approximately of the same level of accuracy for estimating the central venous pressure range, while parameter shock index (at a cutoff point of 1.25) is of the least level of accuracy to predict the central venous pressure range. Results also showed that among all proposed predictive models for estimating the central venous pressure value, which were on the basis of either non-linear regression or artificial neural network, the most accurate model was the one on the basis of the artificial neural network. Among parameters lactate clearance, base excess and shock index used to form the artificial neural network-based model, parameters base excess and lactate clearance were of the highest and lowest level of importance, respectively. Conclusion: Among all proposed models and non-invasive parameters to predict the central venous pressure range, CVP LC model (at a cutoff point of 9), which is a non-linear regression model and is in terms of parameter lactate clearance, was the most accurate model.
Stemming from unfavorable environmental conditions, corrosion can adversely affect the behavior of steel structures and damage them. To investigate this phenomenon and study the failure mode and load bearing capacity of corroded slender steel columns to retrofit them by Carbon Fiber Reinforced Polymer (CFRP), 8 equal-height slender Circular Hollow Section (CHS) column specimens were subjected to corrosive conditions at mid-height and near to bottom supports for 12, 18 and 24 hours, retrofitted by CFRP sheets and then all corroded and retrofitted columns were experimentally tested under axial compressive loading; damage dimensions were different. These specimens and two more were also studied numerically based on the Finite Element (FE) analyses of imperfected models using ABAQUS software. The specimens were first analyzed elastically to find their local and global buckling modes and then inelastically (with nonlinear geometry and material). Experimental and numerical results showed that the main problem with slender columns was their global buckling under compressive loading and corrosion reduced their load bearing capacity and ductility. According to these results, corrosion highly affected the buckling of the corroded area and deformed it axially. Regarding corroded columns retrofitted with CFRP, fibers increased the ultimate load capacity and ductility, delayed buckling of the corroded area, controlled fractures and reduced stresses in the damaged zone.
The present study was aimed to investigate the strength and ductility of welded flange plate (WFP) connections. Using the FE method, 52 WFP connections with different beam overall depths and beam flanges/web slenderness ratios were analyzed. Fragility curves indicated that, for a WFP connection which is designed based on the seismic codes, its strength is of more concern than its ductility. In addition, limiting the width‐to‐thickness ratios of the beam flanges and web plates to and respectively, may not always lead to the achievement of adequate connection’s strength and ductility. Proposed theoretical formulas and artificial neural network‐ (ANN‐) based models developed in this study were able to adequately predict the connection strength.
This study aims to investigate the accuracy of bolt eccentricity (eb) and the required weld size for connecting shear tab to the support presented in 15th edition of AISC Steel Construction Manual for conventional single-plate (CSP) connections. In addition, the available equation for prediction of the weld eccentricity (ew) was evaluated. For this purpose, by changing different parameters, 72 specimens were designed in accordance with the AISC Manual. The designs are in a way that the bolt fracture becomes the governing limit state. Investigated parameters include loading type, bolt pretensioning force, beam span (Lb), beam depth (db), the number of bolts (n) and the spacing between bolt and weld lines (a). All specimens were analyzed through finite element (FE) method using ABAQUS software. Results indicate that the manual prediction for eb is non-conservative and inaccurate. Although the available equation for ew was able to reasonably predict ew, this equation yields to a non-conservative prediction in most cases. Furthermore, results indicate that among all investigated parameters, only n, Lb and a have remarkable effects on eb and ew. In order to propose alternative equations for eb and ew in terms of effective parameters, artificial neural network was utilized which resulted in predictive models with acceptable level of accuracy. Regarding the weld size, a procedure was proposed in which the weld must fail after the bolt fracture. Results show that, using this procedure, leads to a safer weld design in comparison with the use of AISC Manual suggestion for weld design (w = 5/8tp).
Steel structures are damaged for a variety of reasons including accidental loads, corrosion and reduced strength which need to be repaired and improved. In this investigation, local corrosion was applied to the steel circular columns and the effects of Carbon Fiber Reinforced Polymer (CFRP) for strengthening has been studied. 19 specimens of steel Circular Hollow Section (CHS) column with the same height and damage dimensions under compressive load were analyzed by ABAQUS software which six cases of them were performed experimentally. In laboratory cases, progressive corrosion was used to create damage on the specimens. In order to improve the accuracy of the analysis, a combined method was used to study the post-buckling of the plastic zone. For this purpose, the specimens were first subjected to elastic buckling analysis and then Riks non-linear analysis with global and local imperfections was conducted. The results showed that the corrosion reduces the bearing capacity and rigidity of the steel columns and complete destruction of the corroded area reduced the load bearing capacity by 40% for the column with corrosion at the middle and by 21% for the damage close to the base, which shows the former is more critical. Strengthening of columns retrofitted with carbon fibers restored ultimate load reduction by 33% and have a positive effect on controlling fractures and reducing stresses at the damaged area.
In 1994 and 1995, Northridge and Kobe earthquakes caused unexpected damages to beam-to-column connections which were followed by extensive investigations on the connections' behavior to resolve problems in their performance and to improve their strength and ductility. During these years methods were proposed by researchers which were mainly based on reducing the beam section or strengthening the connection. Adding slit dampers at the top and bottom of the beam flanges plates is another way to improve the connection behavior. These dampers are able to absorb and dissipate a significant amount of energy. Slit dampers caused a remarkable reduction in the plastic strain at the column face area and consequently kept plastic hinge formation away from the column face. In this study a total of 8 small slit dampers were used at the column face area. To find out best configuration for slit dampers which can only be used for newly designed connections, a parametric study was carried on their geometry. Generally the slit damper yields in shear or in flexure. Hence, for two different yield mechanisms (shear yielding and flexural yielding) details for designing of slit dampers were proposed and connection's strength and ductility were compared.
Environmental conditions of the Persian Gulf in terms of the durability of the reinforced concrete structures are highly aggressive and corrosive. Hence, in the Persian Gulf and Oman sea areas, based on the national code of practice, concrete durability is controlled by water absorption, water permeability and rapid chloride ion penetration tests. In this research, the above three mentioned tests plus total water absorption test, electrical resistivity, and capillary sorption tests were performed on 216 samples from six concrete mixtures with different water to binder ratios and pozzolan content (fly ash and silica fume). Based on the experimental results, the total water absorption and the water permeability tests were the most and the less accurate tests respectively. Results also showed that the capillary sorption test can be used as a suitable method to evaluate the concrete durability in the marine areas. In this study also a relationship between the specific limits of these tests for different environmental conditions was proposed.
Due to the closed shape of box columns and difficult access to its inside for developing a reliable load path regarding rigid I-beam to box columns connections, in this study, some alternatives have been suggested to replace continuity plates. These alternatives are: two triangular plates, two rectangular plates and added stiff web. To evaluate the efficiency of these suggested alternatives, using ANSYS software, several beam-column connections in each alternative have been modeled. Based on the finite element results the behavior of Ibeam connection to steel box column has been studied. Then the effects of suggested stiffeners on connection stiffness, strength and ductility have been investigated. The results showed that each of the suggested methods might be a good alternative for rigid connection with internal uniform continuity plates. However specimens of additional stiffened webs achieved highest connection strength and ductility.
This paper presents a reduced beam section (RBS) approach via the introduction of two pairs of longitudinal voids in the beam web to enhance the ductility of post-Northridge connections. In order to achieve the highest connection ductility, using finite element method a parametric study was done on the geometry of such voids by considering three different sizes of SAC specimens, SAC3, SAC5 and SAC7. To generalize the design procedure and to make it to be applicable for other beam sections, the suitable equations were proposed to estimate the strain hardening factor, limiting value and ductility of RBS connections with longitudinal voids.
Since the earthquakes in Northridge and Kobe in 1994 and 1995, respectively, many investigations have been carried out towards improving the strength and ductility of steel beam to column pre- and post-Northridge connections. In order to achieve these objectives, recent researches are mainly focused on three principles: reducing the beam section to improve the beam ductility, adding different kinds of slit damper to beam and column flanges to absorb and dissipate the input earthquake energy in the connection and strengthening the connection area using additional elements such as rib plates, cover plates, and flange plates to keep the plastic hinges away from the column face. This paper presents a reduced beam section approach via the introduction of multilongitudinal voids (MLV) in the beam web for various beam depths varying from 450 mm to 912 mm. ANSYS finite element program was used to simulate the three different sizes of SAC sections: SAC3, SAC5, and SAC7. Results showed an improvement in the connection ductility since the input energy was dissipated uniformly along the beam length and the total rotation of the connection was over four percent radian.
This study aims to investigate the adequacy of the ductility requirement presented in the 15th edition of AISC Steel Construction Manual for conventional single-plate (CSP) connections when the threads of the used bolts are excluded from the shear plane (i.e., using X-bolts). For this purpose, by changing different parameters, 72 specimens were designed in accordance with the AISC Manual. All specimens were analyzed based on finite element (FE) method using ABAQUS software. FE results indicated that the most effective parameters which affect the connection rotational demand are loading type and beam length-to-beam depth ratio while connection rotational capacity is mostly affected by the number of bolts, beam depth and bearing strength of beam web/shear tab. To make a more accurate judgment about connection ductility, first, the existing equation for estimating rotational demand, usually leading to a non-conservative prediction, was modified. Then, using the FE results, three predictive models for connection rotational capacity was proposed. Comparing these models showed that the one which was developed on the basis of the artificial neural network is of the highest level of accuracy. Finally, using Monte Carlo method, a reliability analysis was conducted which showed that the ductility requirement of AISC Manual can be too conservative in most cases when the number of bolts exceeds five.
In order to enhance the strength and ductility of post-Northridge connections with beam depths varying from 450 mm to 912 mm, two parallel horizontal long voids were opened on their beams web. Results showed that the proposed beam end configuration (BEC) is effective in moving the plastic hinge away from the column face. Adding web stiffeners and two tubes at the center of voids were effective in preventing excessive beam flange/web buckling. Based on the analytical results a step by step design procedure is proposed to determine the most suitable geometry for the BEC to achieve adequate connection strength and ductility.
Steel slit dampers (SSDs) are replaceable or repairable devices that can be used as a main energy dissipation source. Using SSDs instead of main members such as beam ends in moment frames, most of the deformation concentrate in these devices could make the damaged building repairable. Two main behaviors are expected for a SSD: yielding and buckling. To achieve a remarkable energy dissipation source, the buckling of a SSD must be prevented. The aim of the present study was to predict the force–displacement capacity boundary (FDCB) of an unbuckled SSD, with respect to its type and geometry. Three SSD types (single, double and triple) and five geometric parameters for detailing of a SSD were defined. Using finite element method and different combinations of these parameters, 749 (209 buckled and 504 unbuckled) SSDs were created. Such results could be used to define the appropriate slenderness ratios that represent the buckling behavior of a SSD. Additionally, it may propose appropriate range for the slenderness ratios to ensure that a SSD does not buckle under lateral loads. Furthermore, for each model the associated FDCB was drawn and characterized by three key points: yield, cap and ultimate. To calculate the yield point few theoretical formulas were proposed. Results showed that the theoretical formulas are not enough reliable. Hence, using the finite element results and regression analysis for each SSD type, appropriate formulas that consider all effective geometric parameters were proposed, to predict the force and displacement corresponding to each key point of the FDCB.
