COLUMN base connections are commonly used to connect steel COLUMNs to concrete foundations in seismically designed Steel Moment Resisting Frames (SMRFs). These connections are economical for mid-to high-rise frames in which exposed base plate connections (affixed to the footing with anchor) are impractical owing to the necessity of thick base plates and numerous anchor rods. The bolts are cast into the concrete base in location tubes or cones and fit anchor plates to prevent pullout. High-strength grout is poured into the space below the plate. COLUMN base connections are one of the most critical structural connections. Understanding the behavior and performance of these connections come in handy for designing this type of connections, especially in the seismic design of the structures. Such COLUMN bases are often only subject to axial compression and shear. However, uplift and horizontal shear may be a design case for COLUMN bases in braced bays. The way in which horizontal shear forces are transferred to the foundation is not well researched. Some designers check the resistance of the holding down bolts, and ensure that they are adequately grouted. This practice has been successfully followed for portal frame bases, which carry a significant shear. In COLUMN base connection, it can be said that the rotational STIFFNESS is the only feature that links uncertainty in COLUMN base connection to structures such that a change in them can change rotational STIFFNESS and, as a result, change the dynamic characteristics and seismic response of structures. In the present study, by considering the sensitivity mentioned above, the effects of rotational STIFFNESS and the strength capacity of COLUMN base connection on behavior and seismic performance of steel moment frame have been evaluated by Modal Pushover Analysis (MPA) and Nonlinear Dynamic Analysis (NLDA) methods. The results show that the rotational STIFFNESS of the COLUMN base connection effects on the dynamic properties of structures such as pushover curve, story drift, and ductility as well as the analysis of models together with different rotational STIFFNESS showed that structures in combination with semi-rigid rotational STIFFNESS are much better in designs.

Use of adhesively bonded joints in structures has been increased in recent years because of their advantages. In structural applications, fatigue is generally considered to be the most important form of loading in respect to long-term service life. In this paper, experimental tests have been performed in order to examine the fatigue damage process of double lap adhesive joints, composed of E-glass laminates and epoxy adhesive with TiO2 P25 particles, under fatigue loading and then a method was proposed for fatigue life prediction based on initial STIFFNESS. The scatter in results shows that the fatigue life is mostly dependent on initial STIFFNESS. According to this, an exponential equation based on the initial STIFFNESS has been proposed to have an initial estimation of fatigue life of the adhesive joints. In addition to the initial STIFFNESS, STIFFNESS degradation of the joints under fatigue loading influences on their final performance and therefore the initial estimation of fatigue life based on the initial STIFFNESS could be modified. Also to have an online control of the fatigue damage process during the fatigue loading, a damage index using STIFFNESS degradation was introduced.

The aim of this research work is to study the flexural behaviour of steel beam-COLUMN connection with gusset plate under static loading condition. Connections are normally the focal points of receiving damage due to overload including earthquake. The main reason for the failure of connection is, their inability to deliver large rotation. Gusset plates are used for connecting two or more members together. While gusset plates are used as the connecting element of bracing to the beam-COLUMN joint, the load carrying capacity and STIFFNESS of beam-COLUMN joints are possible to increase. To know the increasing capacity of beam-COLUMN connection with gusset plate are determined by conducting the experimental and analytical program. An experimental research demonstrates the actual behaviour of steel beam-COLUMN connection with gusset plate. There are four number of specimens are tested under static loading condition. Each specimen is fabricated by changing the connection parameter like gusset plate thickness, angle leg length. Finite element analysis was done using ABAQUS. Using the finite element model, a parametric study was conducted to determine the changes in the connection and initiation of damages. The contact element which is used as a surface to surface instead of node to node. Accurate results can be obtained by validating the results of experimental work with FEM analysis. The comparison is made for the deflection and strain occurred on the experimental program with the analytical results.

Pipeline systems under thermal loads are frequently used in different industries, such as the power plants and petrochemicals. Unlike the analytical method of elastic center, which is capable to analyze only one branch of pipeline with pipe members parallel to the coordinate system, the method of STIFFNESS removes these limitations. In this article the STIFFNESS method is introduced for the analysis of pipeline systems. Based on this method, the piping system may include any number of piping braches. The straight pipe elements in the branch may have any general orientation and the bend elements may have any arbitrary angle. The computer program designed based on this method may compute the nodal displacements at the ends of the straight or bend elements and present three components for loads and three components for moments. Once the free-body diagram of each piping elements with nodal forces and moments are drawn, then the engineering codes are employed to design the piping system for safe operation.

The purpose of this review study is to review the studies that have assessed the interaction between surface STIFFNESS and lower limb STIFFNESS. There is a general hypothesis that with the increase of surface STIFFNESS, the lower limb STIFFNESS decreases or vice versa. These interactions take place with the aim of maintaining the dynamics of the center of mass and reducing the energy consumption during movement. One of the mechanisms for these interactions is the change in joint STIFFNESS and leg geometry. Some studies suggested that the stretch reflex has no role in changing the lower limb STIFFNESS. Although interactions between lower limb STIFFNESS and surface STIFFNESS has been recognized, there is little evidence about neuromuscular mechanism of these interactions. More studies is needed in this filed.

In this study, an analytical method is developed to predict the behavior of deficient reinforced concrete beam-COLUMN joints after strengthening. Deficient joint is a joint without shear reinforcement. In this analytical method, different types of failure are estimated using principal stress-strain relationships in the joint and by determining the final capacity of beam and COLUMN. The use of relations between principal stresses in the joint accounts for the variation of the axial stress of the COLUMN in equations and joint capacities. The equations are obtained by considering the strength and deformation limit states in the joint, and a numerical method is employed to solve them. The proposed analytical method provides useful information regarding the strengthened joint capacity as well as how different types of strengthened methods work. This information can be used to select the strengthening method of the deficient joints. In the study, the calculation sequence of beam-COLUMN joints is illustrated using COLUMN axial force versus flexural capacity relationship of the joint members, employed as a criterion to determine the method and the amount of strengthening materials. In the experimental part of the study, 3 specimens with axial load variation and 3 specimens with constant axial load were conducted. The specimens were strengthened using either near-surface mounted steel reinforcement (NSM) or externally bonded reinforcement (EBR) with CFRP sheets. The experimental results indicated that the behavior of joints was significantly affected by considering the COLUMN axial force. Additionally, strengthening the joints by NSM method with steel bars rather than EBR method led to more ductile behavior. Finally, the proposed analytical method was compared with the results of the experimental specimens from other studies and 6 experimental specimens conducted in this study. Comparison of the experimental results with the values of the analytical method demonstrated that the proposed analytical method could adequately predict the behavior of beam-COLUMN joints.

In this paper a new ribbed bracing system (RBS) is proposed capable of performing as a variable STIFFNESS system that can be used for controlling structural deformations and frequency shifting to compensate seismic energy. RBS has two important advantages. Because of ribbed system, the compressive member is rigidly moved like a piston and a cylinder and therefore it is a buckling prevented system. Also it is possible to use this system as a semi-active system by considering the story drifts and global structural damage and control the system if it is necessary to be open or closed based on the operational criteria assigned in the system. RBS has no need to any actuator and large power supply, but just a battery-size power supply to switch the ribbed mechanism to be on or off. RBS is composed of a ribbed supplemental part and a normal wind-bracing on each floor. Considering an appropriate criterion based on the storey drift, minimum number of bracing systems will be active on the height of structure during earthquake. In contrast with completely closed RBS (CC-RBS) by on-off bracing system arranged along the height of the building cause period shifting of the structure to the larger value. Three stages are considered in the numerical studies: conventional bracing frame (CBF), CC-RBS and semi-active RBS (SA-RBS). Damage indices and Fourier transforms are calculated in order to discuss on the efficiency of the proposed system. Nonlinear dynamic analysis of system has been carried out and structural behaviour has been investigated.Numerical results show the efficiency of CC-RBS in reducing structural damage and improving seismic energy. Also base shear is reduced when SA-RBS is used and structural damage is more uniform in this case.