NATIONAL CONFERENCE ON STRUCTURAL ENGINEERING IRAN | Year:2015 | دوره:1 |Papers Count:7

IN THIS PAPER, A NEW EXACT FORMULATION FOR CALCULATING THE ELASTIC BUCKLING LOAD OF SEMI-RIGID STEEL FRAMES WITH TAPERED COLUMNS WILL BE OBTAINED. THE PRESENTED METHODOLOGY IS BASED ON THE PRECISE SOLUTION OF THE GOVERNING DIFFERENTIAL EQUATIONS FOR BUCKLING OF THE UNIFORM AND NON-UNIFORM FRAMES. THEN, THE EFFECTS OF THE NON-PRISMATIC MEMBERS, WITH A PARABOLIC STIFFNESS VARIATION, FLEXIBILITY OF CONNECTIONS, AND LATERAL BRACING ON THE BUCKLING LENGTH FACTOR AND CORRESPONDING CRITICAL LOAD OF A PORTAL FRAME WILL BE INVESTIGATED PARAMETRICALLY. RESULTS SHOW THE COMBINED EFFECT OF AFORENAMED PARAMETER ON THE CRITICAL BUCKLING LOAD AND CORRESPONDING EQUIVALENT BUCKLING LENGTH FACTOR OF PORTAL STEEL FRAMES IS VERY SIGNIFICANT.

THE EXTRACTION OF ORE AND MINERALS BY UNDERGROUND MINING OR OTHER UNDERGROUND WORKINGS OFTEN CAUSE GROUND SUBSIDENCE PHENOMENA. IN URBAN REGIONS, THESE PHENOMENA MAY INDUCE SMALL TO SEVERE DAMAGE TO BUILDINGS. WE HAVE DEVELOPED VULNERABILITY FUNCTIONS FOR DETERMINING DAMAGE TO BUILDING IN SUBSIDENCE REGIONS. THE METHODOLOGY USES MONTE CARLO SIMULATIONS, AND EXISTING ANALYTICAL METHODS BASED ON THE BEAM THEORY FOR THE EVALUATION OF DAMAGE IN THE SUBSIDENCE AREA. IT ALLOWS TAKING INTO ACCOUNT UNCERTAINTIES BOTH ON THE GEOMETRICAL AND MECHANICAL PARAMETERS OF BUILDINGS, AND ON THE PHENOMENA OF SOIL STRUCTURE INTERACTION FOR ANALYTICAL METHODS. THIS PAPER FOCUSES ON UNCERTAINTIES ON SOIL-STRUCTURE INTERACTION. THE DETERMINATION OF DAMAGE WITH ANALYTICAL METHODS REQUIRES VALUES OF THE HORIZONTAL STRAIN AND THE DEFLECTION TRANSMITTED TO BUILDINGS. BUT THE AVAILABLE GEOTECHNICAL PARAMETERS ARE THE HORIZONTAL GROUND STRAIN AND THE GROUND CURVATURE, SOIL STRUCTURE INTERACTION PARAMETERS ARE THEN REQUIRED TO DETERMINE HOW THESE GEOTECHNICAL STRAINS ARE TRANSMITTED TO BUILDINGS. THE VALUE OF THESE LATER PARAMETERS ARE DEPENDENT ON SEVERAL FACTORS, SUCH AS THE SOIL AND THE BUILDING RIGIDITY, THE BUILDING TYPE, THE MINE OR TUNNEL DEPTH, THE LOCALISATION OF BUILDING IN A SUBSIDENCE BASIN. ALL OF THESE FACTORS INCREASE THE UNCERTAINTIES IN BUILDING VULNERABILITY FUNCTIONS, AND MUST BE CONSIDERED IN THE DEVELOPMENT OF THESE FUNCTIONS. WE OBSERVED THAT LOW VALUES OF GROUND CURVATURE COEFFICIENT (KD) LEAD TO A FLATTENING OF THE VULNERABILITY CURVE (LOW VULNERABILITY), AND THAT LOW VALUES OF HORIZONTAL STRAIN SOIL-STRUCTURE INTERACTION COEFFICIENT (KE) LEAD TO A SHIFT OF THE VULNERABILITY CURVE TO THE RIGHT (REDUCED VULNERABILITY). FINALLY, IT ALSO APPEARS THAT THE BUILDING VULNERABILITY CURVES ARE MORE SENSITIVE TO KD VALUES THAN TO KE VALUES.

IN THE PRESENT PAPER, EFFECTS OF INCOHERENCY AND WAVE-PASSAGE ON NONLINEAR RESPONSES OF CONCRETE ARCH DAMS WERE INVESTIGATED. A DOUBLE CURVATURE ARCH DAM WAS SELECTED AS NUMERICAL EXAMPLE. RESERVOIR WAS MODELED AS A COMPRESSIBLE MATERIAL AND FOUNDATION WAS MODELED AS A MASS-LESS MEDIUM. GROUND MOTION TIME-HISTORIES WERE ARTIFICIALLY GENERATED USING MONTE CARLO SIMULATION APPROACH. FOUR DIFFERENT FE MODELS WERE CONSIDERED INCLUDING; UNIFORM EXCITATION; INCOHERENCE EFFECT; WAVE PASSAGE EFFECT AND; FINALLY BOTH INCOHERENCE AND WAVE PASSAGE EFFECTS. IT WAS REVEALED THAT MODELING MULTIPLE-SUPPORTS EXCITATION COULD HAVE SIGNIFICANT EFFECTS ON THE STRUCTURAL RESPONSE OF THE DAM BY INDUCING PSEUDO-STATIC EFFECT. ALSO, IT WAS CONCLUDED THAT COHERENCY EFFECT OVERSHADOW WAVE PASSAGE EFFECT AND RESULTS OBTAINED FROM NON-UNIFORM EXCITING OF FEM INCLUDING WAVE PASSAGE EFFECT IS CLOSE TO THE RESULTS OF THE FE MODEL EXITED UNIFORMLY.

IN THE PRESENT PAPER, THE EFFECT OF NON-UNIFORM EXCITATION DUE TO SPATIALLY VARYING EARTHQUAKE GROUND MOTIONS (SVEGM) ON LINEAR RESPONSES OF CONCRETE ARCH DAMS IS INVESTIGATED. AN ITERATIVE SCHEME IS UTILIZED TO GENERATE SEISMIC GROUND MOTION TIME-HISTORIES AT SEVERAL LOCATIONS ALONG FOUNDATION BOUNDARIES THAT ARE COMPATIBLE WITH PRESCRIBED TARGET RESPONSE SPECTRA AND ARE CORRELATED ACCORDING TO A GIVEN COHERENCE FUNCTION INCLUDING THE WAVE PROPAGATION EFFECT. A DOUBLE CURVATURE ARCH DAM IS SELECTED AS CASE STUDY IN WHICH THE RESERVOIR IS MODELED AS A COMPRESSIBLE MEDIUM AND THE FOUNDATION IS ASSUMED TO BE MASSLESS. VARIOUS LOAD COMBINATIONS ARE CONSIDERED BASED ON THE CORRESPONDING RESERVOIR WATER LEVELS AND THERMAL LOADS. IT IS OBSERVED THAT USING SVEGM LEADS TO HIGHER VALUES IN BOTH TENSILE STRESSES AND PERCENTAGE OF OVERSTRESSED PARTS WITHIN THE DAM BODY IN COMPARISON WITH UNIFORM EXCITATION AND THEREFORE TO BE MORE REALISTIC IN CALCULATING THE DAM RESPONSE, THIS PHENOMENON SHOULD BE INCORPORATED IN SEISMIC ANALYSES ESPECIALLY IN HIGH SEISMICITY REGIONS.

DIFFERENT METHODS ARE USED TO ESTIMATE THE LOCATION AND INTENSITY OF DAMAGE IN STRUCTURES AND THESE METHODS USE DIFFERENT STATIC AND DYNAMIC RESPONSES. EVEN THOUGH MANY METHODS HAVE BEEN PROPOSED FOR DAMAGE DETECTION IN THE LAST TWO DECADES, SENSITIVITY BASED ANALYSES ARE STILL POPULAR. IN THIS RESEARCH, THE EFFECTS OF DIFFERENT RESPONSES IN SENSITIVITY-BASED METHODS, FOR TWO CASES OF ADDITIVE AND MULTIPLICATIVE NOISES IN A TRUSS AND A TWO LAYERS DRAMATIC DOME ARE STUDIED. FIRST, BY IMPOSING NOISE IN VARIOUS RESPONSES AND IMPLEMENTING MONTE CARLO SAMPLING, AN INDEX WAS DEVISED TO EVALUATE THE SENSITIVITY OF EACH RESPONSE TO SENSOR LOCATION. THEN, DIFFERENT RESPONSES ARE USED TO DETECT DAMAGE IN STRUCTURES, BUT SINCE IT IS AN ILL-POSED PROBLEM, TIKHONOV REGULARIZATION SCHEME IS USED TO EVALUATE EXACT RESULTS OF EACH RESPONSE, THROUGH AN UPDATING PROBLEM. BY COMPARING THE RESULTS, IT IS CONCLUDED THAT SENSITIVITY OF STATIC RESPONSES TO SENSORS LOCATION IS LESS AND STATIC RESPONSE IS THE MOST EFFECTIVE RESPONSE WITH FEWER ERRORS IN DAMAGE DETECTION OF THE CASES.

MOTIVATED BY MECHANICAL PROPERTIES AND DURABILITY AGAINST SEVERE EXPOSURE, INCREASING USE OF ULTRA HIGH PERFOMANCE FIBER REINFORCED CONCRETE (UHPFRC) IN THE LAST DECADE HAS OPENNED A NEW HARIZON FOR ENGINEERS AND DESIGNERS IN THE AREA OF CONSTRUCTION. THIS NEW TECHNOLOGY CAN HERALD CHANGE IN CONSTRUCTION INDUSTRY IN THE FUTURE DECADE. THE NEED FOR THE NEW WORLD INFRASTRUCTURE DEVELOPMENT, THE LIMITED RESOURCES AND RAW METERIALS USED, AND THE DESTRUCTIVE ENVIRONMENTAL IMPACT OF RELATED PRODUCTS OF CONSTRUCTION INDUSTRY HAVE SHOWN THE IMPORTANCE OF DOMINATING AN IDEOLOGY BASED ON QUALITY WITH REDUCING ENVIRONMENTAL IMPACT AND INCREASED ECONOMIC EFFICIENCY. UHPFRC, AS A NEW GENERATION OF CONCRETE, HAS BEEN STUDIED BY ENVIRONMENTAL AND ECONOMIC LIFE CYCLES SINCE ITS INCEPTION. THE OBJECTIVE OF THIS STUDY IS TO COMPARE THE ECONOMIC AND ENVIRONMENTAL IMPACT OF UHPFRC BRIDGE CONSTRUCTION WITH NSC BRIDGE CONSTRUCTION IN A PERIOD OF 100 YEARS USING THE LIFE CYCLE ASSESMENT (LCA) METHODOLOGY. THE STUDY HAS BEEN PERFORMED IN AHVAZ, IRAN. THE ANALYSIS SHOWS THAT THE COSTS OF UHPFRC WITHIN 100 YEARS ARE AROUND ONE THIRD OF THE NSC COSTS WITHIN THE SAME PERIOD. THE PESSIMISTIC ESTIMATE OF THE ENIVONMENTAL IMPACT OF UHPFRC ESPECIALLY IN GLOBAL WARMING EQUALS THE NSC IMPACT.

THIS PAPER EXPERIMENTALLY AND INVESTIGATES THE BEHAVIOR OF REINFORCED CONCRETE (RC) COLUMNS SUBJECTED TO ECCENTRIC LOADING WITH EXPERIMENTAL METHODS. THE COLUMNS ARE REINFORCED AND CONFINED WITH CROSS SPIRAL. THE NEW CONFINEMENT TECHNIQUE USES CROSS SPIRALS TO CONFINE RC CIRCULAR COLUMNS IN ORDER TO ENHANCE THEIR STRENGTH AND DUCTILITY. EIGHT RC CIRCULAR COLUMNS SUBJECTED TO LOAD ECCENTRICITY WITH TWO DIFFERENT GRADES OF SPIRALS STEEL, TWO DIFFERENT VOLUMETRIC RATIO OF CONFINING SPIRAL AND TWO DIFFERENT POSITIONS OF CROSS SPIRALS ARE EXPERIMENTALLY TESTED. THE FORCE, AXIAL AND LATERAL DISPLACEMENT AND CONCRETE STRAINS IN DIFFERENT LOCATIONS ARE MEASURED DURING THE TESTING. THE COLUMNS ARE 1000 MM LONG WITH TWO HUNCHED HEADS OF 500 MM HEIGHT AND 250 MM DIAMETER.