Iman Faridmehr

Seismic Performance of RC Beam-Column Connections with Continuous Rectangular Spiral Transverse Reinforcements for Low Ductility Classes

The seismic performance of RC columns could be significantly improved by continuous spiral reinforcement as a result of its adequate ductility and energy dissipation capacity. Due to post-earthquake brittle failure observations in beam-column connections, the seismic behaviour of such connections could greatly be improved by simultaneous application of this method in both beams and columns. In this study, a new proposed detail for beam to column connection introduced as “twisted opposing rectangular spiral” was experimentally and numerically investigated and its seismic performance was compared against normal rectangular spiral and conventional shear reinforcement systems. In this study, three full scale beam to column connections were first designed in conformance with Eurocode (EC2-04) for low ductility class connections and then tested by quasistatic cyclic loading recommended by ACI Building Code (ACI 318-02). Next, the experimental results were validated by numerical methods. Finally, the results revealed that the new proposed connection could improve the ultimate lateral resistance, ductility, and energy dissipation capacity.

Seismic and Progressive Collapse Assessment of New Proposed Steel Connection

The performance of a new proposed steel connection against seismic loading and progressive collapse was experimentally and numerically investigated in this paper. The seismic performance included interstory drift angle and flexural strength evaluated in accordance with 2010 AISC Seismic Provisions whereas progressive collapse assessment was based on satisfaction of the acceptance criteria by rotational capacities of the connection provided in UFC 4-023-03 guideline. The results confirmed that the new proposed connection was capable of achieving adequate rotational capacity and developing the full inelastic capacity of the connecting beam. In addition, an excellent cyclic behavior was demonstrated by proposed connection which enhance interstory drift angle. Based on the results the proposed connection has adequate intensity and ductility to classify it as full-strength and ductile connection.

Classification System for Semi-Rigid Beam-to-Column Connections

THE CURRENT STUDY ATTEMPTS TO RECOGNISE AN ADEQUATE CLASSIFICATION FOR A SEMI-RIGID BEAM-TO-COLUMN CONNECTION BY INVESTIGATING STRENGTH, STIFFNESS AND DUCTILITY. FOR THIS PURPOSE, AN EXPERIMENTAL TEST WAS CARRIED OUT TO INVESTIGATE THE MOMENT-ROTATION (M-I¸) FEATURES OF FLUSH END-PLATE (FEP) CONNECTIONS INCLUDING VARIABLE PARAMETERS LIKE SIZE AND NUMBER OF BOLTS, THICKNESS OF END-PLATE, AND FINALLY, SIZE OF BEAMS AND COLUMNS. THE INITIAL ELASTIC STIFFNESS AND ULTIMATE MOMENT CAPACITY OF CONNECTIONS WERE DETERMINED BY AN EXTENSIVE ANALYTICAL PROCEDURE FROM THE PROPOSED METHOD PRESCRIBED BY ANSI/AISC 360-10, AND EUROCODE 3 PART 1-8 SPECIFICATIONS. THE BEHAVIOUR OF BEAMS WITH PARTIALLY RESTRAINED OR SEMI-RIGID CONNECTIONS WERE ALSO STUDIED BY INCORPORATING CLASSICAL ANALYSIS METHODS. THE RESULTS CONFIRMED THAT THICKNESS OF THE COLUMN FLANGE AND END-PLATE SUBSTANTIALLY GOVERN OVER THE INITIAL ROTATIONAL STIFFNESS OF OF FLUSH END-PLATE CONNECTIONS. THE RESULTS ALSO CLEARLY SHOWED THAT EC3 PROVIDED A MORE RELIABLE CLASSIFICATION INDEX FOR FLUSH END-PLATE (FEP) CONNECTIONS. THE FINDINGS FROM THIS STUDY MAKE SIGNIFICANT CONTRIBUTIONS TO THE CURRENT LITERATURE AS THE ACTUAL RESPONSE CHARACTERISTICS OF SUCH CONNECTIONS ARE NON-LINEAR. THEREFORE, SUCH SEMI-RIGID BEHAVIOUR SHOULD BE USED TO FOR AN ANALYSIS AND DESIGN METHOD.

Cyclic and Explosive Evaluation of New Proposed Steel Joint

The behaviour of a novel steel beam-to-column connection, the saddlebag, subjected to cyclic and progressive collapse, was evaluated in this paper. The cyclic behaviour considered the interstory drift angle and flexural strength in accordance with 2010 AISC Seismic Provisions, while progressive collapse assessment was evaluated through the plastic hinge rotation angle based on acceptance criteria provided in the UFC 4-023-03 guideline. From the cyclic test, one complete cycle of an interstory drift angle of 0.06 rad was satisfied for the saddlebag connection, which is an indication of the effectiveness in accordance with 2010 AISC Seismic Provisions. Besides, the new proposed connection developed adequate catenary action, which is a fundamental criterion to resist against progressive collapse. The resulting fuller hysteretic loops with large energy dissipation capacity in the proposed saddlebag connection guarantee its ability to address the inelastic deformation demands in earthquake conditions.

Seismic Performance of Steel Frames with Semirigid Connections

The nonlinear stiffness matrix method was incorporated to investigate the structural performance of steel portal frames with semirigid connections. A portal frame with unstiffened extended end-plate connection was designed to demonstrate the adequacy of the proposed method. Besides, the seismic performance of steel portal frames with semirigid connections was investigated through time history analysis where kinematic hysteresis model was assigned to semirigid connections to account for energy dissipation and unloading stiffness. Based on the results of the study, it was found that generally semirigid connections influenced the force distribution which resulted in the decrease in base shear and lighter frame compared to the rigid one. The results also indicated that there was no direct relationship between maximum displacement at the top and connection stiffness in high-rise frames.

Effect of Web Holes and Bearing Stiffeners on Flexural-Shear Interaction Strength of Steel Cold-Formed C-Channel Sections

This paper presents an investigation on interaction equation between the required flexural strength, M, and the required shear strength, V, of cold-formed C-channels with web holes and bearing stiffeners. The primarily shear condition test was employed to study total 8 back to back lipped C channel sections of 95 and 100 mm depth when bearing stiffeners and circular holes were placed at center and both ends of specimens. The interaction equation were evaluated via Direct Strength Method, DSM, in accordance with the American Iron and Steel Institute for the design of cold-formed steel structural members, AISI 2007. A nonlinear finite element model was developed and verified against the test results in terms of failure buckling modes. It was concluded that the M-V interaction equation for specimens with web stiffeners was conservative where these specimens experienced plastic failure mode rather than local (Msl) or distortional (Msd) buckling mode. Moreover, the results indicated that proposed M-V interaction equation calculated by local buckling strength (Msl) adequately predicted the behavior of specimens with circular web holes.

Severe Loading Assessment of Modern and New Proposed Beam to Column Connections

The performance of two different steel beam to column connections known as SidePlateTM and a new proposed connection by seismic loading and progressive collapse were investigated in this research. Seismic performance evaluated included consideration of interstory drift angles and flexural strengths based on 2010 AISC Seismic Provisions while investigation of progressive collapse was conducted through satisfaction of acceptance criteria by rotational capacities of the connections provided in UFC 4-023-03 guideline. The results indicated that both SidePlate and the new proposed moment connection were capable of achieving adequate rotational capacity and developing full inelastic capacity of the connecting beam. Also, an excellent performance was exhibited by the connections in terms of keeping the plastic hinges away from the connection and exceeding interstory drift angle of 0.06 rad without fracture developments in beam flange groove-welded joints. Based on results, it was concluded that the SidePlate and the new proposed connection possess sufficient stiffness, strength and ductility to be classified as rigid, full-strength and ductile connections.

Modification of grout properties in prepacked aggregate concrete incorporating palm oil fuel ash

Prepacked aggregate concrete (PAC) is a type of concrete that is placed in two stages where the coarse aggregates are first placed inside the formworks and then the grout is pumped from underneath through a manual pump. Grout properties including density, grout consistency, bleeding, and compressive strength are of great importance in PAC. Such properties could be improved by application of pozzolanic materials like palm oil fuel ash. This paper is aimed at finding the most optimum percentage of POFA replacement by weight of cement. It was concluded that 30% POFA replacement yielded the most optimum results.

Procjena ponašanja "Pre-Northridge" priključaka na ekstremna opterećenja

Katastrofalne posljedice djelomicnog urusavanja apartmana Ronan Point 1968. i potresa u Northridgeu 1994. razotkrile su osjetljivost celicnih okvira izloženih ekstremnim opterecenjima. Izvjesca ovih dvaju katastrofalnih događaja pokazala su znacajnu ulogu prikljucka nosac-stup gdje su se pretežno događala ostecenja. Numericko i eksperimentalno istraživanje provedeno je u skladu sa 2010 AISC seizmickim odredbama i UFC 4-023-03 smjernicama. Nisko ciklicno ponasanje i rotacijski kapacitet proizlaze iz analize gdje je lom u blizini suceonog zavara bio nacin otkazivanja uzoraka.