Artículos científicos

THE CLT MARKET IS QUICKLY GROWING AND DEVELOPING IN DIFFERENT REGIONS OF THE WORLD. HOWEVER, THE PRODUCTION AND CONSUMPTION ARE HIGHLY CONCENTRATED IN CENTRAL EUROPE (AUSTRIA, GERMANY, ITALY, AND SWITZERLAND). DUE TO THE ELEVATED LEVELS OF PERSONALIZATION REQUIRED FOR THE CONSTRUCTION PROJECTS, THE CLT MANUFACTURING PROCESS INVOLVES COSTLY AND SPECIALIZED EQUIPMENT THAT REPRESENTS AN ENTRY BARRIER FOR DOMESTIC PRODUCERS IN MARKETS WHERE THE DEMAND IS SMALL AND INCIPIENT. THIS WORK DISCUSSES A PRODUCTION MODEL AND SUPPLY CHAIN INTEGRATION FOR THE DEVELOPMENT OF THE CLT INDUSTRY IN EMERGING ENVIRONMENTS WHERE THE PRODUCT AND ITS PROPERTIES ARE NOT WELL-KNOWN. FURTHERMORE, A COMPREHENSIVE ECONOMIC ANALYSIS IS PERFORMED FOR THREE SMALL CAPACITY MILLS DESIGNED ACCORDING TO SMES CAPABILITIES. FINDINGS SUGGEST THAT CLT MANUFACTURING WITH LOW-CAPACITY PLANTS (LESS THAN 10,000 M3/YR) IS PROFITABLE BUT HIGH LEVELS OF INTEGRATION ARE REQUIRED. THE MOST INFLUENTIAL VARIABLES IN THE ECONOMIC RESULTS ARE THE LUMBER COST AND PRODUCTION VOLUME; THEREFORE, SPECIAL ATTENTION MUST BE PAID TO THE EFFICIENCY OF THE PROCESS. DESPITE THE SMALL SIZE OF THE STUDIED PLANTS PROMOTED BY THE PROPOSED PRODUCTION AND PLANT DESIGN MODEL, THE SALE PRICE IS ATTRACTIVE AND COMPETITIVE.

CROSS-LAMINATED-TIMBER (CLT) STRUCTURES HAVE GAINED POPULARITY IN THE FIELD OF MEDIUM-RISE BUILDINGS DUE TO THE QUICK FABRICATION AND ASSEMBLY OF THE PANELS. HOWEVER, CONNECTIONS IN RADIATA PINE CLT SHEAR WALLS AND THE BEHAVIOR OF CLT STRUCTURES UNDER LATERAL LOADS IS STILL NOT WELL UNDERSTOOD. IN THIS CONTEXT, THIS PAPER STUDIES THE STRUCTURAL BEHAVIOR OF HOLD-DOWN CONNECTIONS ON RADIATA PINE CLT WALLS BY MEANS OF EXPERIMENTAL TESTS AND NUMERICAL SIMULATIONS UNDER STATIC AND DYNAMIC CONDITIONS. THE TEST RESPONSE OF CONNECTIONS WAS REPLICATED BY CALIBRATING TWO HYSTERETIC MODELS ON OPENSEES. THE MAIN RESULTS SHOWED THAT APPLIED MODELS CAN REPRODUCE THE HYSTERETIC BEHAVIOR OF HOLD-DOWN CONNECTIONS WITH HIGH PRECISION. IT WAS OBSERVED THAT HOLD-DOWN CONNECTIONS ON RADIATA PINE CLT WALLS REACHED A LOADING CAPACITY SIMILAR TO OTHER WOOD SPECIES, BUT THE STRENGTH AND STIFFNESS DEGRADATION WAS QUICKER, AND NO SIGNIFICANT DIFFERENCE WITH THE PARALLEL TO GRAIN CAPACITY OF ANGLE BRACKET CONNECTIONS WAS NOTICED. IN ADDITION, IT WAS FOUND THAT RADIATA PINE CLT WALLS CAN ACHIEVE SUITABLE CYCLIC LOADING PERFORMANCE WITH LOW DAMAGE LEVEL IN CONNECTIONS AND REACH HIGH LEVELS OF DISPLACEMENT DUCTILITY. FINALLY, THE IMPORTANCE OF FRICTION IN THE LOAD CAPACITY OF THE WALL WAS ALSO SHOWN.

THIS STUDY EXAMINES EXPERIMENTALLY AND NUMERICALLY THE IN-PLANE BEHAVIOR OF A STEEL-SPLINE CROSS-LAMINATED TIMBER (CLT) CONNECTION WITH SELF-TAPPING SCREWS. ALTHOUGH THIS CONNECTION IS A STRONG, RAPID, AND COST-EFFECTIVE ALTERNATIVE SUITABLE FOR CLT DIAPHRAGMS OF TALL TIMBER-CONCRETE BUILDINGS, NO PREVIOUS CYCLIC/MONOTONIC TESTING HAS BEEN DOCUMENTED. TWO SPECIMENS WERE TESTED UNDER AXIAL AND IN-PLANE SHEAR LOADS, WHERE A DUCTILE FAILURE MODE WAS OBSERVED DUE TO BENDING AND WITHDRAWAL OF SCREWS, AND DEFORMATION AND BUCKLING OF THE STRAP. MECHANIC PROPERTIES, SUCH AS STRENGTH CAPACITY, STIFFNESS, DUCTILITY, ENERGY DISSIPATION, EQUIVALENT VISCOUS DAMPING, STIFFNESS/STRENGTH DEGRADATION, AND DAMAGE INDEX CHARACTERIZE THE JOINT. FURTHERMORE, THE YIELD POINT AND DUCTILITY WERE CALCULATED WITH THE EEEP, CEN, AND YASUMURA-KAWAI METHODS, THE LAST APPROACH MOST ACCURATE, WITH A MEAN DUCTILITY OF 7.25 AND 5.50 FOR THE AXIAL AND IN-PLANE SHEAR TESTS, RESPECTIVELY. OVERSTRENGTH FACTORS OF ABOUT 2.6 AND 1.9 WERE ALSO ESTIMATED FOR RESPECTIVE TESTS BY COMPARING ANALYTICAL EXPRESSIONS FROM TIMBER CODES AND LITERATURE. FINALLY, THREE NUMERICAL MODELS (SAWS, DOWELTYPE, AND ASPID) WERE ASSESSED TO MEASURE THEIR EPISTEMIC UNCERTAINTY, SHOWING AN ADEQUATE FORCE AND DISSIPATED ENERGY HISTORY SIMULATION, WITH A NORMALIZED ROOT MEAN SQUARE LESS THAN 8.8% AND 4.5%, AND R(2 )OVER 87% AND 97%, RESPECTIVELY.

SINCE THE LARGE SEISMIC DEMANDS IN CHILE, THERE IS A HIGH LEVEL OF UNCERTAINTY REGARDING THE SEISMIC SAFETY BEHAVIOR OF TIMBER STRUCTURES. BESIDES, IN THE LAST DECADE, THERE HAS BEEN A WORLDWIDE RISE IN THE CONSTRUCTION OF CROSS-LAMINATED TIMBER (CLT) BUILDINGS, EXPLAINED BY THE EASE OF INDUSTRIALIZATION OF CLT PANELS AND FOR BEING A SUSTAINABLE MATERIAL. HOWEVER, ITS MASSIFICATION IN HIGH EARTHQUAKE-PRONE ZONES IS STILL UNDER DEVELOPMENT. THIS RESEARCH ANALYZES THE SEISMIC FRAGILITY OF A 5-STORY CLT BUILDING. THE AIM OF THIS RESEARCH IS TO DETERMINE THE SEISMIC SAFETY LEVEL OF A CLT MIDRISE BUILDING DESIGNED BY CHILEAN FORCE-BASED CODE REGULATIONS BY MEANS OF STATIC NONLINEAR ANALYSIS AND INCREMENTAL DYNAMIC ANALYSIS. FOR IDA CURVES, A SET OF 540 NONLINEAR TIME-HISTORY ANALYSES WERE PERFORMED USING PARALLEL COMPUTING TOOLS. THE MAIN RESULTS SHOW THAT FOR THE COLLAPSE OF THE BUILDING TO OCCUR, LARGE PSEUDO-ACCELERATION VALUES NEED TO BE REACHED. BESIDES, THE COLLAPSE MARGIN RATIO (CMR) IS CALCULATED FOR THE TWO PRINCIPAL DIRECTIONS, ACHIEVING VALUES LARGER THAN 3 FOR 50% COLLAPSE PROBABILITY. THESE RESULTS SUGGEST A LARGE MARGIN OF SEISMIC SAFETY OF THE CLT BUILDING DESIGNED IN THIS RESEARCH.

THIS PAPER PRESENTS A METHODOLOGY TO EVALUATE THE DAMAGE IN CLT WALLS BY APPLYING NON-DESTRUCTIVE VIBRATION-BASED METHODS. THE MAIN CONTRIBUTION IS THAT THE METHODOLOGY ALLOWS LOCATING THE DAMAGE AND ESTIMATING THE SEVERITY OF DAMAGE IN THE DIFFERENT WALL JOINTS, GOING BEYOND THE TYPICAL GLOBAL DAMAGE DETECTIONS. ONE OF THE RELEVANT ASPECTS WAS THE NOVEL COMBINATION OF OPERATIONAL MODAL ANALYSIS, FINITE ELEMENT MODEL UPDATING, AND REGIONAL SENSITIVITY ANALYSIS. THE METHODOLOGY WAS SUCCESSFULLY APPLIED TO A 2-STORY CLT MODULE BUILT IN THE LABORATORY AND INSTRUMENTED WITH ACCELEROMETERS. THE WALL WAS EVALUATED IN 11 DIFFERENT DAMAGE SCENARIOS INDUCED BY INCREMENTAL PSEUDO-STATIC LATERAL LOADS. THE RESULTS OBTAINED CORRELATED REASONABLY WELL WITH THE VISUALLY OBSERVED DAMAGE, SO IT IS ESTIMATED THAT THIS METHODOLOGY COULD BE EXTENDED TO MORE COMPLEX CLT WALL CONFIGURATIONS.

THE SEISMIC ANALYSIS OF MASS TIMBER STRUCTURES THROUGH NUMERICAL MODELS IS CHALLENGING DUE TO THE SYSTEM'S LARGE NUMBER OF NONLINEAR COMPONENTS AND THE COMPLEX FAILURE MECHANISMS DEVELOPED. ADDITIONALLY, IF LONG-DURATION MEGATHRUST EARTHQUAKE RECORDINGS NEED TO BE CONSIDERED, THE TIME CONSUMPTION OF THE COMPUTATION INCREASE SIGNIFICANTLY. THEREFORE, REFINED AND ADVANCED NONLINEAR NUMERICAL MODELS THAT DEMAND HIGH COMPUTATION CAPACITY NEED TO BE CONSIDERED. IN ORDER TO ANALYZE THE LATERAL BEHAVIOR OF CROSS-LAMINATED-TIMBER STRUCTURES, DETAILED COUPLED THREE-DIMENSIONAL NUMERICAL MODELS WERE DEVELOPED IN OPENSEESMP. EVERY COMPONENT OF THE CLT SYSTEM WAS INCLUDED (WALLS, SLABS, SCREWS, AND MECHANICAL CONNECTIONS), AS WELL AS THE FRICTION AND CONTACT INTERACTION AT THE FOUNDATION FLOOR SLABS AND THE WALL-TO-WALL INTERFACE. THE NUMERICAL MODELS? SIZE WAS AROUND 120.000 DOF. IN THIS RESEARCH, SEQUENTIAL AND PARALLEL MODELING TECHNIQUES WERE COMPARED USING STANDARD DESKTOP PCS (8 CORES I7 PROCESSOR). FOR THE IMPLEMENTATION OF THE PARALLEL MODELS, A STATIC DECOMPOSITION APPROACH WAS USED. EIGHT AND THREE CORES WERE EMPLOYED TO PERFORM THE ANALYSES; THEREFORE, THE PARALLELIZATION CONSIDERS THE SEGMENTATION INTO THREE AND EIGHT SUBDOMAINS, RESPECTIVELY. A TOTAL OF 6-TIME HISTORY ANALYSES USING LONG-DURATION SUBDUCTION EARTHQUAKE RECORDINGS FOR EACH CASE OF STUDY WERE PERFORMED. MAIN RESULTS SHOW THAT THERE IS A 50%-TIME REDUCTION IN THE PARALLEL WITH RESPECT TO THE SEQUENTIAL MODELING APPROACH. HOWEVER, INCREASING FROM THREE TO EIGHT PROCESSING CORES MARGINALLY IMPROVES THE PERFORMANCE OF THE NUMERICAL MODELS.

TIMBER STRUCTURES HAVE GAINED INTEREST FOR THE CONSTRUCTION OF MID-RISE BUILDINGS, BUT THEIR SEISMIC PERFORMANCE IS STILL A MATTER UNDER DEVELOPMENT. IN THIS STUDY, A NUMERICAL ANALYSIS OF THE SEISMIC PERFORMANCE OF LIGHT-FRAME TIMBER BUILDINGS IS DEVELOPED THROUGH A HIGHLY DETAILED MODEL USING PARALLEL COMPUTING TOOLS. ALL OF THE LATERAL-LOAD-RESISTING SYSTEM COMPONENTS AND CONNECTIONS ARE MODELED. COMBINATIONS OF LATERAL LOAD CAPACITY DISTRIBUTIONS IN STRUCTURES OF ONE, THREE, AND FIVE STORIES ARE STUDIED IN ORDER TO ASSESS THE EFFECTS ON THE GLOBAL PERFORMANCE OF DIFFERENT TRIGGERED FAILURE MODES THROUGH NONLINEAR STATIC AND DYNAMIC ANALYSES. THE RESULTS SUGGEST THAT SHEAR BRACKET CONNECTIONS AND SHEATHING-TO-FRAMING CONNECTIONS CONTROL THE BUILDINGS? RESPONSES, AS WELL AS THE FAILURE MODE. FOR A DUCTILE RESPONSE, THE LATERAL DISPLACEMENT MUST BE DOMINATED BY THE IN-PLANE WALL DISTORTION (RACKING); THEREFORE, THE SYSTEM MUST BE PROVIDED WITH A STORY SHEAR SLIDING STIFFNESS AND LOAD CAPACITY AT LEAST TWICE THAT OF THE WALLS. FURTHERMORE, BASED ON THE PUSHOVER CAPACITY CURVES, THE PERFORMANCE LIMITS ARE PROPOSED BY EVALUATING THE STIFFNESS DEGRADATION. FINALLY, THE EFFECT OF THE MOBILIZED FAILURE MODE ON THE STRUCTURAL FRAGILITY IS ANALYZED. EVEN THOUGH STANDARD DESKTOP PCS ARE USED IN THIS RESEARCH, SIGNIFICANT REDUCTIONS IN THE COMPUTATION EFFORT ARE ACHIEVED.

THE CONSTRUCTION OF BUILDINGS WITH CROSS-LAMINATED TIMBER (CLT) PANELS HAS GROWN STEADILY IN RECENT YEARS, MAINLY BECAUSE OF THE ENVIRONMENTAL ADVANTAGES OF WOOD OVER OTHER BUILDING MATERIALS. HOWEVER, THERE ARE STILL DOUBTS ABOUT THE DYNAMIC BEHAVIOR OF CLT BUILDINGS IN COUNTRIES WITH HIGH SEISMICITY AND HOW THEIR DYNAMIC PROPERTIES VARY WITH TEMPERATURE AND RELATIVE HUMIDITY CHANGES. THE PRESENT WORK SHOWS THE MODAL PROPERTIES? MONITORING OF A 5-STORY CLT BUILDING PROTOTYPE. THE PROTOTYPE BUILDING IS LOCATED IN CHILE AND HAS DIMENSIONS OF 4.04 M, 6.44 M, AND 14.5 M FOR WIDTH, LENGTH, AND HEIGHT, RESPECTIVELY. THE CLT PANELS ARE MADE OF RADIATA PINE WOOD, AND THE JOINTS BETWEEN PANELS WERE EXECUTED WITH SELF-DRILLING SCREWS AND METAL HARDWARE (HOLD-DOWN AND ANGLE-BRACKET). THE CLT BUILDING WAS INSTRUMENTED WITH TEN UNIAXIAL ACCELEROMETERS (MODEL PCB393B12) DISTRIBUTED ON DIFFERENT FLOORS AND DIRECTIONS TO MEASURE THE LATERAL DYNAMIC RESPONSE TO ENVIRONMENTAL VIBRATIONS. THE FIVE MAIN FREQUENCIES, DAMPING RATIOS, AND MODAL SHAPES WERE ESTIMATED THROUGH THE OPERATIONAL MODAL ANALYSIS METHODS EFDD AND SSI. PRELIMINARY RESULTS SUGGEST THAT, ON AVERAGE, THE LATERAL AND TORSIONAL FREQUENCIES MEASURED IN THE CLT BUILDING WERE BETWEEN 3.13 HZ AND 13.88 HZ. THESE EXPERIMENTAL RESULTS WILL ALLOW A PROCESS OF CALIBRATION AND UPDATING OF FINITE ELEMENT MODELS OF THIS TYPE OF BUILDINGS FOR THEIR SUBSEQUENT INCORPORATION INTO CHILEAN STRUCTURAL DESIGN REGULATIONS.

CROSS-LAMINATED TIMBER (CLT) BUILDINGS HAVE EMERGED AS AN ALTERNATIVE TO MAKE MORE SUSTAINABLE AND RESILIENT CITIES. HOWEVER, VERY FEW CASES OF VIBRATION-BASED MONITORING OF THESE BUILDINGS HAVE BEEN REPORTED. THIS PAPER DISCUSSES THE VARIATION OF THE DYNAMIC PROPERTIES OF A 5-STORY CROSS-LAMINATED TIMBER (CLT) BUILDING THROUGH VIBRATION-BASED MONITORING OVER 23 MONTHS. THE BUILDING COMBINES DIFFERENT CONSTRUCTION SYSTEMS, IS RELATIVELY SLENDER FOR ITS TYPE, AND WAS BUILT IN A HIGH SEISMICITY ZONE. THE MONITORING STRATEGY INCLUDED PERIODIC MEASUREMENTS OF THE DYNAMIC PROPERTIES DURING CONSTRUCTION, REFERENCE MEASUREMENTS WITH HIGH-SENSITIVITY ACCELEROMETERS, AND 10 MONTHS OF CONTINUOUS MEASUREMENTS WITH LOW-COST EQUIPMENT. IN ADDITION, CONTINUOUS MEASUREMENTS ALLOWED THE ANALYSIS OF THE DYNAMIC PROPERTIES DURING SPECIAL EVENTS ASSOCIATED WITH WIND GUSTS AND MODERATE-INTENSITY EARTHQUAKES. DURING THE CONSTRUCTION STAGE MONITORING AND REFERENCE MEASUREMENTS, UP TO 5 MODAL SHAPES OF THE BUILDING WITH THEIR RESPECTIVE VIBRATION FREQUENCIES AND DAMPING RATIOS WERE DETECTED. THESE DYNAMIC PROPERTIES ALLOWED THE CALIBRATION OF A SIMPLIFIED NUMERICAL MODEL OF THE BUILDING. SUBSEQUENTLY, DURING THE CONTINUOUS MONITORING PHASE OF THE BUILDING, IT WAS OBSERVED THAT THE FIRST TWO TRANSLATION FREQUENCIES VARIED BY UP TO 8% DUE TO CHANGES IN CLIMATIC CONDITIONS AND THE MOISTURE CONTENT OF THE TIMBER. FINALLY, MONITORING DURING A 5.4 MW EARTHQUAKE SHOWED THAT VIBRATION FREQUENCIES TEMPORARILY DECREASED BY UP TO 15% AND RETURNED TO THEIR INITIAL VALUE AFTER THE SEISMIC EVENT HAD PASSED. THE RESULTS OF THIS RESEARCH WILL CONTRIBUTE TO THE KNOWLEDGE OF THE DYNAMIC RESPONSE OF THIS TYPE OF BUILDING AND THE UPDATING OF THEIR STRUCTURAL DESIGN CODES.