CONFERENCE ON EARTHQUAKE AND STRUCTURE | Year:2014 | دوره:5 |Papers Count:8

EXPOSED BASE-PLATES TOGETHER WITH ANCHOR BOLTS ARE THE CUSTOMARY METHOD OF CONNECTION OF STEEL STRUCTURES TO THE CONCRETE FOOTINGS. POST KOBE STUDIES REVEALED THAT THE EMBEDDED COLUMN BASES RESPOND BETTER TO THE EARTHQUAKE UPLIFT FORCES. THE EMBEDDED COLUMN BASES ALSO, OFFER HIGHER FREEDOM IN ACHIEVING THE REQUIRED STRENGTH, RIGIDITY AND DUCTILITY. THE PAPER PRESENTS THE RESULTS OF THE PULL-OUT FAILURE OF THREE EMBEDDED IPE140 SECTIONS, TESTED UNDER DIFFERENT CONDITIONS. THE NUMERICAL MODELS ARE THEN, GENERATED IN ABAQUS 6.10-1 SOFTWARE. IT IS CONCLUDED THAT, THE STEEL PROFILES COULD BE DIRECTLY ANCHORED IN CONCRETE WITHOUT USING ANCHOR BOLTS AS PRACTICED IN THE EXPOSED CONVENTIONAL COLUMN BASES. SUCH EMBEDDED COLUMN BASES CAN DEVELOP THE REQUIRED RESISTANCE AGAINST PULL-OUT FORCES AT LOWER CONSTRUCTIONAL COSTS.

THE EXPERIENCES OF THE PAST EARTHQUAKES HAVE BEEN INDICATED THAT THE SURFACE STRUCTURES WERE INFLUENCED BY SEISMIC WAVES ACCORDING TO THE DISTANCE FROM FAULT FOCUS AFTER TUNNEL EXCAVATION. SO THE EFFECTS OF NEAR AND FAR FIELD EARTHQUAKES ON THE SURFACE STRUCTURES SHOULD BE NOTED WHILE UNDERGROUND TUNNELS ARE EXCAVATED. IN THIS ATTEMPT, SATURATED CONDITIONS ARE CONSIDERED SURROUNDING THE EXCAVATED TUNNEL AND THE FINITE ELEMENT MODELING WERE PERFORMED USING COULOMB'S FAILURE EQUATION. THE NONLINEAR TIME-HISTORY ANALYSIS WAS UNDERTAKEN VIA NEAR AND FAR FIELD EARTHQUAKES AND RAYLEIGH DAMPING COEFFICIENTS. THE OBTAINED RESULTS DEMONSTRATE THE STRUCTURES IN VICINITY OF TUNNELS WERE MARKEDLY DAMAGED DUE TO FAR FIELD EARTHQUAKES IN THE SATURATED CONDITIONS AND RESONANCE PHENOMENON ALSO WAS APPEARED.FURTHERMORE STATISTICAL RESULTS SHOW THAT SURFACE STRUCTURES IN THE SATURATED CONDITIONS HAVE EFFECTED NEAR FIELD EARTHQUAKES IN COMPARISON WITH FAR FIELD EARTHQUAKES WHICH THERE IS A SIGNIFICANT DIFFERENCE BETWEEN THE OBTAINED NUMERICAL RESULTS (P-VALUE < 0.05).

THE OPTIMIZATION OF STRUCTURE (OPTIMAL DESIGN) HAS GROWN RAPIDLY OVER THE PAST DECADES WITH MANY DIFFERENT OPTIMIZATION METHODS THAT COULD BE USED TO PRODUCE A STRUCTURE OF MINIMUM WEIGHT. A NEW METHOD OF STRUCTURAL OPTIMIZATION IS THE EVOLUTIONARY STRUCTURAL OPTIMIZATION METHOD. THE NUMBER OF APPLICATIONS OF THE EVOLUTIONARY STRUCTURAL OPTIMIZATION METHOD HAVE EXHIBITED THAT IT IS A VERY RELIABLE AND EASILY APPLICABLE METHOD OF STRUCTURAL OPTIMIZATION. THEREFORE, THE OPTIMIZATION OF SUPPORT CONDITIONS TO MINIMIZE THE WEIGHT OF PLATE STRUCTURES BY THE EVOLUTIONARY STRUCTURAL OPTIMIZATION METHOD IS INVESTIGATED IN THIS PAPER. THE EFFECT OF DIFFERENT BOUNDARY CONDITIONS IS ASSESSED. FINALLY, SOME NUMERICAL EXAMPLES ARE SHOWN TO ILLUSTRATE THE EFFICIENCY AND SIMPLICITY OF EVOLUTIONARY STRUCTURAL OPTIMIZATION METHOD.

ULTIMATE STATE OF STRUCTURAL MEMBERS HAS BEEN WIDELY USED FOR THE PURPOSE OF SEISMIC DESIGN AND REHABILITATION IN SEISMIC STANDARDS. EVEN, COMMON DAMAGE INDICES SUCH AS PARK AND ANG USE ULTIMATE STATE OF STRUCTURAL RESPONSE, KNOWN AS ULTIMATE DEFORMATION. THIS DEFORMATION CAN BE EXPRESSED AS DISPLACEMENT OR, ROTATION AND, CURVATURE OF FLEXURAL MEMBERS. IN THIS STUDY, CORRELATION BETWEEN ULTIMATE CURVATURE AND DEPTH OF I AND, H SHAPED STRUCTURAL STEEL SECTIONS HAS BEEN INVESTIGATED AND, A SIMPLE RELATIONSHIP TO ESTIMATE ULTIMATE CURVATURE IS PRESENTED. IT IS SHOWN THAT, THIS RELATIONSHIP IS ACCURATE ENOUGH TO REPLACE THE TIME CONSUMING PUSHOVER ANALYSES TO OBTAIN ULTIMATE CURVATURE OF MENTIONED SECTIONS.

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.

AN ITERATIVE PROCEDURE BASED ON THE CONCEPT OF UNIFORM DISTRIBUTION OF DEFORMATION IS CONSIDERED TO ACHIEVING OPTIMUM DISTRIBUTION OF BRBS AREA AND THE STIFFNESS OF TADAS FOR REHABILITATION OF A VULNERABLE STRUCTURE AND RESULTS ARE COMPARED WITH HEURISTIC METHODS. PUSHOVER METHOD IS USED FOR ANALYZING MODELS. VULNERABLE STRUCTURE IS A THREE STORY MOMENT FRAME WHICH IS EQUAL IN GEOMETRY AND LOADING CONDITION TO SAC-FEMA THREE STORY BUILDING. IT IS SHOWN THAT BECAUSE OF USING ENGINEERING INTELLIGENCE AND ITS HIGH SPEED IN FINDING OPTIMUM SOLUTIONS, THE UNIFORM DISTRIBUTION OF DEFORMATION METHOD IS AN EFFICIENT METHOD IN COMPARISON WITH HEURISTIC METHODS.

OPTIMIZATION BASED ON THE THEORY OF UNIFORM DEFORMATION IS AN APPROACH WHICH HAS BEEN INTRODUCED IN RECENT YEARS FOR OPTIMIZATION OF STRUCTURES. ALTHOUGH THIS METHOD HAS BEEN PROPOSED AS AN OPTIMIZATION TECHNIQUE, BUT SO FAR THE RESULTS OF THAT HAVE NOT BEEN COMPARED WITH OTHER OPTIMIZATION METHODS. THIS STUDY DEALS WITH PERFORMANCE-BASED DESIGN OPTIMIZATION (PBDO) USING THEORY OF UNIFORM DEFORMATION, AND THE RESULTS COMPARED WITH OTHER OPTIMIZATION TECHNIQUES SUCH AS METAHEURISTIC ALGORITHMS. PUSHOVER ANALYSIS OF THREE STORY MODEL BUILDING DESCRIBED IN SAC PROJECT IS PERFORMED FOR OPTIMIZATION PROCESS. IN THIS STUDY, IT IS INDICATED THAT THE NUMBER OF ANALYSES NEEDED TO OPTIMIZE THE STRUCTURE USING THEORY OF UNIFORM DEFORMATION IS MUCH LOWER THAN THOSE NEEDED FOR METAHEURISTICS.

IN MOST STRUCTURAL SOFTWARES, THE DESIGN PARAMETERS ARE DEFINED AS DETERMINISTIC PARAMETERS SO, THE OBTAINED FREQUENCIES ARE DETERMINISTIC BUT NOT RELIABLE. FOR UNDERSTANDING THE OUTPUT FREQUENCY’S ACCURACY OBTAINED FROM A SOFTWARE, THE PROBABILITY DISTRIBUTION OF FREQUENCY IS NEEDED WHICH IS HERE THE CASE. IN THIS WORK, THE PROBABILITY DISTRIBUTION OF FREQUENCY IS DERIVED BY MONTE CARLO SIMULATION. TO REDUCE THE COMPUTATIONAL TIME, THE NATURAL FREQUENCIES ARE EVALUATED USING TWO METHODS: (1) A LINEAR REGRESSION MODEL, (2) AN EFFICIENT ALGORITHM WITH FIRST AND SECOND ORDER APPROXIMATIONS. FINALLY THE PAPER, THE EFFICIENCY OF THE PROPOSED METHODS IS DISCUSSED THROUGH AN ILLUSTRATIVE EXAMPLE.