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Cement-stabilized macadam is a type of heterogeneous and discontinuous material. To study the mesomechanical behavior of cement-stabilized macadam particles, a discrete-element model of cement-stabilized macadam is constructed according to the random distribution theory and certain porosity and gradation. The constitutive relations of contact between particles may be linear contact, linear bonding, and linear parallel bonding. The stress–strain, crack propagation, particle velocity, stress transfer, and force chain distribution of cement-stabilized macadam were analyzed after comparing the results of simulated uniaxial compression with laboratory tests. The results of uniaxial compression calculations for cement-stabilized macadam were in good agreement with the experimental data. At the beginning of loading, the upper/lower particles moved toward the middle; at the peak loading stage, the particle movement was mainly in the vertical direction; and at the final of loading, the particles mainly moved to the sides. With the increase in loading, the contact force between particles became larger and larger. At the loading peak, the contact force between particles reached the maximum value, and the normal and tangential contact forces of particles were not evenly distributed. Microcracks at each stage were mainly vertical cracks, most of which were located at 70–110°. In this paper, the uniaxial compression test of cement-stabilized macadam was dynamically simulated using discrete-element theory, and the mesoscopic structure and dynamic variation process of parameters were analyzed. It provides references for the study of damage of heterogeneous and discontinuous quasi-brittle materials. [ABSTRACT FROM AUTHOR]

The flexural behavior of hybrid timber–steel encased beams comprising coniferous radiata pine (Pinus radiata) (MGP10) and Douglas fir (Pseudotsuga menziesii) (F8) timber lamellae with bonded-in steel bars is studied. The effect of cross-section depth, steel bar size, timber species/grade, and steel bar arrangements (only bottom and top-and-bottom) on the hybrid beams' stiffness, failure mode, ductility, and load-carrying capacity were investigated. The flexural capacity and stiffness of the doubly (top-and-bottom) reinforced beams are increased by 127% and 71%, respectively. However, in the singly (bottom) reinforced beams, the flexural capacity and stiffness are increased only by 41% and 25%, respectively, highlighting the important role of the compressive bars. The failure of all beams was associated with tensile flexural failure of timber, but the steel bars improved the ductility of the beams. The maximum coefficient of variation of the peak load in hybrid beams (CoV=14.3%) is lower than that of the bare timber beams (CoV=21.7%). Two analytical models were developed based on a linear and a bilinear stress–strain relationship for timber. The analytically predicted peak load and stiffness agree well (less than 13% and 12% difference) with the experimental results. [ABSTRACT FROM AUTHOR]

Textile-reinforced ultrahigh-toughness cementitious composite (UHTCC) jackets––herein referred to as TRU jackets––are an innovative strengthening system for reinforced concrete (RC) structures. The ductile UHTCC used for this jacket system exhibits better deformation compatibility with the textile than brittle mortar does. In this paper, we present an experimental study of the seismic performance of RC columns strengthened with TRU jackets using cyclic lateral loading tests. The results indicated that the TRU jacket could effectively restrain the development of cracks in the plastic hinge zone, delay stiffness deterioration, and significantly improve ductility and energy dissipation. Moreover, at a low stirrup ratio of 0.39%, the peak load of the jacketed columns was greatly enhanced compared to the peak load of the RC companion columns. With an increased number of textile layers, seismic performance was improved. When the ratio of axial force to axial capacity was increased from 0.15 to 0.30, ductility and energy dissipation did not drop for the TRU-jacketed columns. As the strengthening height decreased from 2.0 to 1.2 times the cross-sectional height of the columns, the seismic performance of the jacketed columns remained almost unchanged. A numerical model was developed for the seismic simulation of TRU-jacketed columns, and the predicted hysteresis curves agree well with the test data. [ABSTRACT FROM AUTHOR]

The numerical modeling of thermomechanical fracture is an essential aspect of designing critical components in various industries, including aerospace, automobile, and nuclear. The phase-field method is a suitable approach for simulating thermomechanical fracture problems. However, this method can be computationally expensive. In this study, we propose a multilevel adaptive mesh refinement (ML-AMR) using a phase-field approach, for thermomechanical fracture problems. The proposed approach can efficiently and accurately capture the crack topology without the need for any pre-refinement or explicit marking of damage boundary. Our proposed ML-AMR algorithm introduces an error estimator based on effective crack driving energy computed based on thermomechanical loading using the three prominently used phase-field models (AT2, AT1, and PF-CZM). We demonstrate the accuracy and computational efficiency of the proposed method by simulating various thermomechanical fracture problems and comparing the results with the nonadaptive phase-field method that adopts a priori nonadaptively refined meshes. We consider different types of thermal and mechanical loading, including thermal shock, to evaluate the proposed approach comprehensively. Our results show that the proposed ML-AMR phase-field method reduces computation time by 78%–99% while accurately capturing the crack path, peak load, and total strain energy. [ABSTRACT FROM AUTHOR]

This work presents an experimental study performed to investigate the effect of the size of the specimen on the fracture response of geometrically similar concrete notched beams. To the best of the authors' knowledge, this study is the largest of its kind and includes beams of five different sizes. Twenty-eight beams were tested using a three-point bending (TPB) test setup designed according to draft guidelines. Five depths D , namely, 75, 150, 250, 500, and 1,000 mm, were considered, and the width b was kept constant and equal to 150 mm for all specimens. A new setup is proposed for large specimens. Load responses, peak loads, failure modes, fracture energy, and size-effect analysis are presented and discussed. [ABSTRACT FROM AUTHOR]

The main objective of this study is to investigate the effect of moisture damage on the fatigue and cracking behaviors of warm mix asphalt (WMA) containing reclaimed asphalt pavement (RAP). To achieve this aim, different fatigue and cracking tests such as indirect tensile fatigue failure, four point beam fatigue, and semicircular bending tests have been conducted, and several parameters have been obtained. These parameters include tensile strength ratio (TSR) and fracture energy ratio (FER), indirect tensile fatigue ratio (IDTR), peak load ratio (PLR), J-integral ratio, and flexibility index (FI), and Nf and flexural stiffness ratios. The results showed that moisture-damaged RAP-WMA demonstrated slightly weaker fatigue and cracking resistance than other mixtures, which is not significant considering the environmental advantages of the mixture. Hence, RAP-WMA would be a proper and beneficial alternative as pavement material where there are significant problems in supplying natural aggregates, and issues like moisture damage and being environment friendly are big concerns. Also, it has been concluded that the fatigue test condition (stress and strain control modes) had a significant effect on the moisture damage investigation. [ABSTRACT FROM AUTHOR]

Acoustic emission (AE) technology has advantages in characterizing the damage of asphalt mixture and its microcrack formation and development. In this study, AE characteristic parameters and high-speed camera recording results were combined to explore the cracking process, fracture propagation characteristics, and fracture modes of asphalt mixtures with different gradations under different loading rates. The test results show that the crack propagation process of an asphalt mixture can be divided into four stages: elastic deformation, damage accumulation, crack propagation, and failure. After the crack propagation stage, the crack path of the asphalt mixture changes from the interface between coarse aggregate and asphalt mortar to the pass-through coarse aggregate. The peak load, AE count, density of peak frequency points, and proportion of peak frequency in a higher frequency range for an asphalt mixture increase with the increase of loading rate and the decrease of nominal maximum size of aggregate. The change of loading rate affects the number of peak frequency bands, but the nominal maximum size of aggregate has no effect on the number of peak frequency bands. The peak frequency mainly distributes in low and mid-low frequency. Under semicircular bending (SCB), tensile fracture is the main failure mode and shear failure is the secondary failure mode for an asphalt mixture with prefabricated cracks. With the increase of loading rate and nominal maximum size of aggregate, the number of tensile cracks decreases and the number of shear cracks increases in an asphalt mixture. [ABSTRACT FROM AUTHOR]

Full-scale model tests of three integral prestressed prefabricated frame structure system (IMS) prestressed friction joint specimens under low cyclic loading were conducted to explore the factors influencing the hysteretic behavior of a new joint. The use of a high-strength grouting material (steel fiber) for joints was found to delay the damage of the grouting material under repeated loads and cause reduction of effective prestress. Additionally, replacing the prestressed reinforcement with unbonded prestresssed reinforcement in the precast column and the open channel near the column maximized the deformation capacity of the structure and reduced the structural damage and stiffness degradation in later stages. With an increase in the length of the unbonded section, the peak load of the specimen decreased and the energy consumption was worsened. To enhance the energy consumption of the joint, this study proposes a hybrid connection joint between the energy-consuming and prestressed reinforcements in the open slot. Using ABAQUS numerical modeling and analysis, the joint structure was further optimized and the variations in the energy consumption capacity of the hybrid joint with the position of the prestressed reinforcement, the proportions for the local weakening of energy-dissipating reinforcement, and the bonding mode were obtained. The numerical results demonstrated that the seismic performance index of the hybrid joint was comparable to or even higher than that of the cast-in-situ joint and indicated excellent self-centering and damage recover capacity. [ABSTRACT FROM AUTHOR]

Steel frames may have an inherent ability to resist progressive collapse through alternative load-resisting mechanisms, including Vierendeel, flexural, catenary, and membrane actions. Among the columns at different positions, corner column failure caused by accidental loading is more dangerous due to the relatively few alternative load-resisting mechanisms. To evaluate the effects of infilled walls with or without openings on the progressive collapse resistance of steel frames, four two-span 2-story steel frames were tested in this study. According to the test results, the solid infilled frames achieved peak loads that were over 300% greater than those of the bare frame. Relative to the bare frame, the infilled frames with solid bricks and perforated bricks increased the deflection capacities by 15% and 29%, respectively. This result was attributed to the development of effective compressive struts in the infilled walls to partially transfer the vertical loads. Thus, premature joint failure was avoided. Moreover, the failure modes of the infilled walls changed when different types of brick were adopted. The infilled walls with solid bricks showed extensive shear sliding cracks; the infilled walls with perforated bricks were relatively intact, but the compressive corners were crushed. The partially infilled frame with a 40% opening ratio still increased the load-resisting capacity of the steel frame by 90%. In addition, the efficiencies of the compressive strut models of the infilled walls under corner column loss conditions were evaluated. Based on the calculations, the width of the equivalent compressive strut provided by current US standards is recommended. [ABSTRACT FROM AUTHOR]

Embedded plates (EPs) are commonly used to connect steel to reinforced concrete elements. Due to a lack of industry-wide standard designs, EPs are custom designed for every instance in each project. This leads to many inefficiencies in the construction process and introduces susceptibilities to error. North American design standards based on the concrete capacity design (CCD) philosophy require many assumptions to predict EP capacity, which then lead to inconsistencies in their application. CCD is also well suited for analysis as it depends on a considerable numbers of variables (e.g., edge distances, anchor size, number, and length) to check capacity. The sheer number of variables makes it difficult for designers to come up with a trial design to fit a situation. This study aims to improve the efficiency of this process by proposing standard EPs. A subset of these proposed standard EPs are then experimentally tested to verify predicted capacities and evaluate design assumptions using existing CCD approaches in North America. Four- and six-anchor proposed standard EPs with shear tab connections were placed at four distances from the concrete edge (75–250 mm) and tested in shear towards the edge. North American provisions for concrete anchorage were adequate in predicting the failure loads if connection eccentricity, caused by the gap between the shear tab bolt line and the exposed surface of the plate, is considered in capacity predictions. Mean test-to-predicted ratios of 0.92 and 1.05 were obtained, respectively, when not considering and considering this eccentricity. Rotations of these connections during testing (0.01 to 0.02 rad at peak load with further rotations post-peak) and signs of secondary tension breakout cones suggest that connection eccentricity significantly affects the behavior of EPs and should be considered in design. [ABSTRACT FROM AUTHOR]

We investigate the generalization of a convolutional neural network (CNN)-based surrogate for the phase field model in predicting both damage and peak load under uniaxial tension, given the two-dimensional (2D) microstructure image of a unidirectional fiber–reinforced composite. We first discuss the phase field model and the numerical procedure to generate training and test data from synthetic microstructures with different volume fractions and fiber radiuses. We next present a two-stage approach for predicting peak load, achieved by first transforming a given fiber-encoded microstructure image to a continuous damage field; and second, predicting peak load from the damage field. A key finding is that the direct approach for predicting peak load from the microstructure image using a standard regression model fails to generalize. Instead, the damage field, even if imperfectly predicted, provides valuable cues for the CNN in generalizing across new microstructures within the range of parameters used in training. We describe several case studies to demonstrate the capability of the surrogate model to predict damage and peak load, and to interpolate over fiber radiuses and volume fractions. [ABSTRACT FROM AUTHOR]

Concrete-filled double-skin tube (CFDST) columns are considered one of most efficient forms of steel-concrete composite columns, which provide higher axial strength and better ductility compared with their counterpart concrete-filled tube (CFT) columns. This paper aims to numerically investigate and compare the performance of axially loaded circular CFDST short columns provided with stiffeners in inner tubes and outer tubes. Circular steel hollow sections have been adopted for inner as well as outer tubes, and rectangular steel stiffeners were fixed in inner and outer tubes to check the effectiveness of stiffeners in stiffened CFDST columns. These CFDST columns were investigated numerically by using a verified finite-element (FE) model from commercially available software. Behavior of 36 unstiffened, inner-tube stiffened, and outer-tube stiffened CFDST columns (12 each) was studied. The FE results were verified by comparing them with previous test results. The FE analysis study has exhibited an increase in peak load (load-carrying capacity) up to 26% and 15% in outer-tube stiffened CFDST columns compared with unstiffened and inner-tube stiffened CFDST columns, respectively. Also, enhanced ductility has been observed in case of these stiffened CFDST columns. [ABSTRACT FROM AUTHOR]

In this study, a total of 10 steel and glass fiber–reinforced polymer (GFRP) bar–reinforced normal strength concrete (NSC) specimens with a square cross section of 200 mm × 200 mm were experimentally tested up to failure under different loading conditions. Out of the 10 specimens, 8 specimens had a height of 800 mm and were tested as columns under concentric and eccentric axial loads. The remaining two specimens had a length of 1,500 mm and were tested as beams under four-point bending. The tested specimens were utilized to investigate the efficiency of carbon fiber–reinforced polymer (CFRP) strip ties (CSTs) in transversely confining NSC specimens. Two configurations of CSTs were used: a square (S) configuration and a square overlapping square (SS) configuration. The experimental results indicated that the peak axial load and ductility of the concentrically loaded GFRP bar–reinforced concrete specimens were lower than those of steel bar–reinforced specimens. The peak axial load and ductility of the concentrically loaded GFRP bar–reinforced concrete specimens with SS configuration were about 49% and 100%, respectively, higher than those of GFRP bar–reinforced concrete specimens with S configuration. Also, the GFRP bar–reinforced concrete specimens tested under eccentric loading and four-point bending achieved higher peak axial loads, flexural loads, and bending moments at the second peak loads than the corresponding steel bar–reinforced specimens. [ABSTRACT FROM AUTHOR]

The peak load on a borehole wall is a key parameter in calculating the blasting failure range and in numerical simulations of nonfluid–structure coupling. In this study, the characteristics of the peak load in water-coupling blasting are studied theoretically and numerically. First, the interaction between a waterborne shock wave and a borehole wall is analyzed theoretically to reveal the main factors in the peak load on the borehole wall. Then, based on the theoretical calculations and the principle of dimensional homogeneity, a calculation model for the peak load is determined, and a numerical simulation of fluid–structure coupling is carried out to obtain the peak load under different conditions in two types of water-coupling blasting. The theoretical and numerical results are compared, and a correction coefficient is introduced to optimize the theoretical model. The results showed that the peak load increases approximately as a power function with increasing rock wave impedance and decreases approximately as a power function with increasing decoupling coefficient. Furthermore, it is concluded from statistical analysis that the correction coefficient is linearly proportional to the decoupling coefficient. In summary, a method for calculating the peak load on a borehole in water-coupling blasting is proposed, and it is verified against existing stress test data from water-coupling blasting. [ABSTRACT FROM AUTHOR]

An equivalent static analysis (ESA) procedure is proposed for the design of pile-supported wharves subjected to combined inertial and kinematic loads during earthquakes. The accuracy of the ESA procedure was evaluated against measurements from five large-scale centrifuge tests. The wharf structures in these tests were subjected to a suite of recorded ground motions and the associated superstructure inertia, as well as earthquake-induced slope deformations of varying magnitudes. It is shown that large bending moments at depths greater than 10 pile diameters were primarily induced by kinematic demands and can be estimated by applying soil displacements only (i.e., 100% kinematic). In contrast, the large bending moments at the pile head are primarily induced by wharf deck inertia and can be estimated by applying superstructure inertial loads at the pile head only (i.e., 100% inertial). Large bending moments at depths shallower than 10 pile diameters are affected by both inertial and kinematic loads; therefore, evaluation of pile performance should include soil displacements and a portion of the peak inertial load at the pile head that coincides with the peak kinematic loads. Ranges for inertial and kinematic load combinations in uncoupled analyses are provided for different soil profiles. The details on the back-calculated load combination factors are provided in the companion paper. [ABSTRACT FROM AUTHOR]

Five dynamic, large-scale centrifuge tests on pile-supported wharves were used to investigate the time- and depth-dependent nature of kinematic and inertial demands on the deep foundations during earthquake loading. The wharf structures in the physical experiments were subjected to a suite of recorded ground motions and imposed superstructure inertial demands on the piles. Partial to full liquefaction in loose sand resulted in slope deformations of varying magnitudes that imposed kinematic demands on the piles. It was found that the wharf inertia and soil displacements were always in phase during the critical cycle when bending moments were at their maximum values. The test results were analyzed to provide the relative contributions of peak inertial loads and peak soil displacements during critical cycles, and the data revealed the depth dependency of these factors. The results of this study are used in a companion paper to provide recommendations for the design of pile-supported wharves subjected to foundation deformations. [ABSTRACT FROM AUTHOR]

Inconsistency and large scatter are widely observed in comparisons between experimentally obtained and analytically predicted shear capacity contributed by fiber-reinforced polymer (FRP) composites in FRP-strengthened reinforced concrete beams using existing codes and models. Shear crack configuration, overlooked by many design codes, guidelines, and analytical models, can possibly attribute to such a scatter and inconsistency. To that end, an innovative analysis approach was proposed, in combination with a conducted experimental study, to investigate the effect due to such a shear crack configuration. It was found that large axial rigidity of the FRP reinforcement and the shear span-to-effective depth ratio tended to create distributed shear cracks, which changed the shear behavior of strengthened beams by decreasing the bond length and the resultant FRP shear contribution. The strain of the shear reinforcement increased with the increase of the crack width, which reached the peak value after the peak load level. Since not all steel stirrups yielded, the shear contribution of the concrete itself was greatly underestimated. It is suggested to propose separate sets of design equations corresponding to different categories of shear crack to improve the precision and minimize such a scatter. [ABSTRACT FROM AUTHOR]

Masonry-infilled wood frame walls are widely used in vernacular buildings all over the world. Based on traditional European wood frame walls, this paper proposes wood bracing as reinforcement for traditional Chinese masonry-infilled wood frame walls to compensate for premature cracking of masonry infill and the resulting performance degradation of the walls. Five wall frames were prepared and loaded cyclically in lateral direction. Wood bracings of different forms and their contribution to the wall performance were studied. The hysteretic curves, stiffness and strength degradation, energy dissipation, and equivalent viscous damping coefficient were determined and discussed for their relationship with the bracing provisions. It was found that the bare frame was flexible and resilient and the masonry-infilled frame was stiff and prone to brittle failures, while the frames reinforced by wood bracing exhibited good load-carrying capacity, deformability, and energy dissipation capacity. The peak load and the ultimate displacement of the frame reinforced by X-bracing were 49% and 85% higher than those of the masonry-infilled frame, and the equivalent viscous damping coefficient was increased by 81% at most. The asymmetric Z-bracing and double crossing bracing led to a slight decrease in the initial stiffness compared to the masonry-infilled frame due to the pull-out of the intermediate mortise-tenon connections. [ABSTRACT FROM AUTHOR]

Devastating natural hazards induced by the propagation of extremely rapid, flow-like fragmented rocks can be reduced or even avoided by protective structures in the corresponding danger areas. Such barriers are expected to store the mass before it threatens the vulnerable infrastructures. Proper designs are required by calculating the peak impact force of granular flows on the barriers. In this work, a discrete element method (DEM) was validated with a physical experiment. Sixty simulations were carried out using DEM to study the flow regime governing the dynamic response of granular flows against the barrier. Results reveal that the inertial number (I) can demarcate the flow regime into dense and dilute flow. For the dense flows (I < 3), the equation based on the hydrodynamic model is much more efficient. For the dilute flows (I > 3), the Hertz contact method is better at calculating the peak load. The aforementioned findings are expected to be convenient for engineers designing mitigation constructions against flow-like hazards in mountain areas. [ABSTRACT FROM AUTHOR]

The Brazilian tension test is the most common tension test used for concrete, with the advantage of simple setup. However, cracking in the Brazilian test takes place abruptly, which does not allow monitoring of postpeak behavior and crack propagation. In this paper, a novel experimental testing technique that enables monitoring of postpeak cracking behavior using the Brazilian tension test is described. The technique uses additional spring supports in parallel to the test specimen to offload the test specimen incrementally. When the concrete specimen reaches its peak load, the spring supports will resist approximately 80% of the machine load. As the concrete specimen cracks, its stiffness drops, and the spring system increasingly carries more of the load. The load on the specimen is continuously reduced, which slows crack propagation. Comparison with the standard Brazilian tension test without springs shows that the proposed test does not affect the concrete behavior precracking or postcracking but slows down postpeak crack propagation and thus allows monitoring of postpeak concrete behavior in tension. [ABSTRACT FROM AUTHOR]

This paper summarizes preliminary results of an experimental investigation on the creep behavior of transverse welded lap joints at elevated temperatures. The aim of this study is to quantify the time-to-failure for transverse welded lap joints exposed to high temperatures. In this study, two series of experiments were conducted. In the first series, the specimens were heated to target temperatures and then loaded to failure to estimate the peak load P that the specimens could sustain at each target temperature. In the second series, after the specimens were heated to the test temperatures, fractions of the peak load P were applied rapidly and kept constant throughout the test. Through the combination of these two series of experiments, the effect of load and temperature on the time-dependent or creep behavior of transverse welded lap joints was studied. The experimental results show that, for temperatures greater than 450°C, transverse welded lap joints undergo excessive deformation due to creep, and that creep effect becomes more significant as load and temperature increase. [ABSTRACT FROM AUTHOR]

Ten large-scale high-strength concrete (HSC) circular columns were constructed and tested to failure. Nine columns were internally reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals, whereas one was reinforced with steel bars and spirals to serve as a reference. All columns had a diameter of 350 mm. The variables tested were reinforcement type, spiral pitch, slenderness ratio, eccentricity-to-diameter ratio (e/D), and type of loading (axial or four-point bending). Experimental results showed that both reinforcement types (steel or GFRP) and the spiral pitch did not have a significant effect on the behavior of GFRP-reinforced HSC columns up to the peak load. In addition, a decrease in the axial capacity of the columns as the e/D ratio increased was observed. This was consistent for specimens of both slenderness ratios of 14 and 20. Columns with a higher slenderness ratio showed a lower axial capacity for all specimens tested under the same e/D ratio. Furthermore, slender columns with higher e/D ratio underwent much larger deformations; both axially and laterally. For columns of both slenderness ratios, axial load–bending moment interaction diagrams were produced using the experimental results and were compared to the predictions of available codes and guidelines. [ABSTRACT FROM AUTHOR]

Heavy glulam timber framed structures are facing a growing inadequacy in resisting lateral actions from earthquakes and winds due to the increasing building heights. This paper presents the experimental and numerical analysis results on the hysteretic behavior of newly developed carbon fiber reinforced polymer (CFRP) confined timber-steel buckling-restrained bracings and the lateral performance of bolted glulam timber frames with such bracings. Ten timber-steel bracings and four frames with different bracing provisions were tested via reversed cyclic lateral loading. A finite-element method based model was developed, verified, and used for parametric studies. The bracing test results indicated that the design requirements for ordinary buckling restrained bracings on the confinement ratio and the transverse bulging force are adequate for the proposed timber-steel bracings. A confinement ratio no less than 4.6 is suggested. Compared to an otherwise similar bare frame, two frames with the proposed bracings were found to be 132% and 176% higher in the peak loads, more than 10 times higher in the elastic stiffness, 40% and 43% higher in ductility ratio, and on average 106% higher in the equivalent viscous damping ratio. The two frames also exhibited higher stiffness and energy dissipation than a frame braced by timber bracings, which are prone to buckling failure. Parametric studies indicated that the secant stiffness and the damping ratio of the frames at small drift can be substantially affected by the bolt slippage of the bracing-frame connections. The increased lateral stiffness ratio will lead to increase in the peak load and stiffness, but the equivalent viscous damping ratio remains nearly constant for lateral stiffness ratios larger than 2.5. The frame stiffness and peak load increase with increased rotational stiffness of the beam-column connections while the equivalent viscous damping ratio decreases. [ABSTRACT FROM AUTHOR]

Due to the increasing tendency to construct taller and more slender buildings, the need to address aerodynamic and induced dynamic forces (inertial forces) under both service and strength-level wind loads has become more important. Currently, application of performance-based wind design (PBWD) to reduce induced dynamic forces applied through the acceptance of inelastic deformation is permitted as an alternative design approach, in which wind load can be reduced with respect to the yield strength and ductility of the structure. However, reduced wind load smaller than aerodynamic forces may not ensure proper inelastic wind design. The results of this study indicate that to avoid huge ductility demand due to damage accumulation, the yield strength for structural systems with zero-to-modest post-yield stiffness must be larger than the aerodynamic forces. Moreover, due to uncertainty in the number of occurrences of peak aerodynamic loads applied to a structure during a wind event, it would be advisable for systems with large post-yield stiffness to consider upper limits of aerodynamic forces. [ABSTRACT FROM AUTHOR]

A slab-column joint in a flat plate structure may exhibit upward or downward punching shear (UPS and DPS) failure when subjected to different abnormal loading conditions. This can cause distinct residual deformations of the slabs, which in turn influences the behavior of the consequent progressive collapse of the entire structure. This paper presents two experimental tests on two 2×2-bay , 1/3-scaled flat plate substructure specimens. Both tests were conducted in two loading phases. In the first loading phase (LP-1), the interior column of specimens UPS-Sub and DPS-Sub was subjected to a gradually increased upward and downward concentrated load, respectively, until punching failure occurred at the interior slab–column joint. In the second loading phase (LP-2), an incremented downward uniformly distributed load was applied on the slab of both specimens up until the ultimate state just before a complete collapse of the slab. After LP-1, local and global damage patterns were observed respectively from UPS-Sub and DPS-Sub. The punching shear strength and the corresponding displacement of the interior joint in UPS-Sub were found to be 58.2% higher and 53.6% lower, respectively, than the corresponding ones in DPS-Sub. In LP-2, due to the upward residual deformation of the slab in UPS-Sub as a result of LP-1, its first peak load, vertical displacement, and horizontal displacement under compressive membrane action were, respectively, 8.4%, 91.1%, and 57.1% larger than those in DPS-Sub. On the other hand, the postpunching peak load of the two specimens under tensile membrane action were identical. To offer an in-depth understanding of the mechanical behavior that resulted from upward or download punching shear failure, the punching shear strengths of the interior slab–column joints and collapse resistance of the substructures were also analytically investigated. [ABSTRACT FROM AUTHOR]

Ultrahigh-performance concrete (UHPC) typically contains short steel fibers with a fiber volume of 2% or larger. This relatively high fiber volume leads to high UHPC tensile strength, typically larger than 8 MPa, and constitutes 30%–40% of the UHPC material cost. Recent studies show that if the reinforcing ratio is low, the high tensile strength of UHPC results in a low structural drift capacity (e.g., less than 2.5%). To lower the cost and improve the ductility of steel-reinforced UHPC (R/UHPC), this study experimentally and numerically explores the relationship between R/UHPC flexural behavior and UHPC material tensile behavior, which is affected by the fiber volume. Experimental variables include reinforcing ratios (0.96% and 2.10%), fiber volumes (0.5%, 1%, and 2%), and two proprietary UHPC materials. Seven simply supported R/UHPC beams are tested. Experimental results show that (1) reducing the fiber volume has little impact on the maximum crack width at the service limit state and the crushing resistance at the ultimate limit state; and (2) with a low reinforcing ratio, reducing fiber volume increases the structural member ductility and provides more failure warnings at the peak load. To understand the relationship between R/UHPC flexural behavior and more possible variations of material properties, a two-level, five-factor factorial experiment was conducted numerically with different combinations of reinforcing ratios, reinforcing steel properties, and UHPC tensile properties. Numerical results show that higher reinforcing ratios, higher steel postyield hardening strength, and lower UHPC tensile strength lead to a more ductile flexural failure. Finally, a minimum reinforcing ratio is validated to mitigate the possibility of low structural drift capacity (e.g., less than 2.5%). [ABSTRACT FROM AUTHOR]

The link between the fracture behavior of fiber–reinforced concrete composite and the underlying mechanisms that influence the pullout behavior of fiber are studied. The influence of the fiber-matrix bond on the cohesive stress response in fracture is evaluated for normal vibration compacted concrete (NC) and self-compacting concrete (SCC) matrixes. The fracture response of steel fiber–reinforced SCC (SFSCC) improves significantly when compared with steel fiber–reinforced NC (SFNC). The cohesive stress-crack opening (σ−w) relationship derived from the measured fracture responses indicates that a significantly higher crack closing stress is generated at smaller crack opening in SFSCC than SFNC. The pullout resistance of the steel fiber embedded in the SCC matrix improves significantly compared with NC. The enhancements in the cohesive debonding and frictional components of resistance contribute to the improved pullout resistance of the steel fiber from SCC. The improvement in the fiber-SCC matrix bond results in increased efficiency of the fibers and produces an increase in stiffness and peak load in the resistance to the pullout of fiber from the SCC matrix when compared with NC. The enhancement in the pullout response of the fibers from SCC contributes to improvements in the cohesive stress mobilized at smaller crack openings in SFSCC. [ABSTRACT FROM AUTHOR]

In fabric-reinforced cementitious matrix (FRCM) systems, one technique to increase the strengthening efficiency is to utilize the deformability of dry fiber bundles and anchor them at their ends. In this study, the effectiveness of anchored carbon fiber bundles was thoroughly investigated through pull-out tests of 220 specimens and corresponding microstructural analyses. The results show that the peak pull-out load can be increased by up to 165% after anchoring the fiber bundles, and the dominant failure mode shifts from fiber pull-out to fiber rupture. Parametric analyses show that a larger anchorage angle and a larger total embedded length help to increase the pull-out strength, while a proper combination of the bonded length and the anchorage length is essential for high strengthening efficiency. Further microstructure analyses suggest that these improvements are primarily attributed to the additional constraint at the anchorage point, and the anchorage length is critical for the pull-out behavior. [ABSTRACT FROM AUTHOR]

Over the past decade, cross-laminated timber (CLT) panels have gained popularity worldwide. To achieve larger spans and to increase the resistance to diaphragm seismic and wind forces to be transferred through CLT floor or roof systems, CLT-concrete composite (CCC) floors have been developed as an alternative. While significant testing has been performed under gravity loading, limited experimental data exist on the in-plane performance of CCC systems. This study presents results from an experimental program designed to characterize the in-plane shear behavior of CCC diaphragm connections using different CLT to concrete screw connector orientations in a test setup that simulates the expected seismic load path in diaphragms for platform-type construction. Tested variables include concrete slab thickness, composite screw angle, and single spline connection systems consisting of nails or screws. Experimental results and observed damage progression from cyclic testing are presented and discussed. Results indicate that CCC systems achieved increased stiffness and strength values when compared to bare-CLT systems, but slab thickness did not influence the strength and stiffness of the system for the load paths simulated. Additionally, CCC floor systems with 45° composite screw connectors displayed increased strength but overall similar stiffness values when compared to the CCC systems with 90° composite screws. The results provide useful engineering parameters, such as elastic stiffness, peak load, displacement capacity, and ductility ratios that can be used in the development of codified design parameters or in performance-based designs. [ABSTRACT FROM AUTHOR]

When a steel frame is subjected to an abnormal load, a sudden local failure due to the loss of a load carrying member may result in progressive collapse of the entire structure. In this study, experiments and numerical simulations were performed to investigate the anti-collapse performance of double half-span assemblies (a column connected with two half-span beams) with welded unreinforced flange–bolted web (WUF-B) connections in a column removal scenario. Three types of bolted webs—two bolts in one row, three bolts in one row, and four bolts in two rows—were considered. For the post-peak response, the connections exhibited a significant resistance recovery owing to the catenary action. The bolt-bearing areas on the beam web were prone to fracture owing to excessive compression, and the failure modes of the web varied significantly with the bolt arrangement. The test results demonstrate that increasing the number of bolt rows is a fairly effective approach for enhancing the anti-collapse performance of the WUF-B connections. Numerical models were used to further investigate the effects of the bolt arrangement on the anti-collapse performance of the WUF-B connections. The results indicate that the bolt arrangement can directly affect the response of the connections after the first peak load, especially in the catenary phase. [ABSTRACT FROM AUTHOR]

During winter, energy piles are subjected to cooling cycles due to the cyclic operation of the ground source heat pump (GSHP). The cyclic operation of the heat pump causes the energy pile to contract and expand axially and radially, affecting the soil–pile interaction. The effects of cooling cycles on the thermomechanical behavior of energy piles have not been fully investigated. A fully instrumented model concrete energy pile was installed in dry sand and subjected to cooling cycles. Cooling was achieved by circulating a heat exchange fluid with a target inlet temperature of 20°C lower than the initial temperature of the soil (ΔT=−20°C). Following the application of thermal loading, pull-out axial load tests were performed to evaluate the effects of cooling cycles on the load–displacement response of the energy pile. Baseline (room temperature), 5-cooling-cycle (5CC), and 100-cooling-cycle (100CC) tests were performed and summarized in this paper. During the thermal and mechanical load applications, temperature in the soil and the pile, axial strains, radial strains, and radial pressures at the soil–pile interface were measured. For the 1g scaled energy pile and test conditions (pile in dry sand subjected to cooling cycles with ΔT=−20°C), the peak pull-out loads decreased by 32% and 38% for the 5CC and 100CC tests, respectively. [ABSTRACT FROM AUTHOR]

The experimental results for large-scale slender circular reinforced concrete (RC) columns are presented and discussed in this study. One reference column was reinforced with steel bars and spirals, and five columns were reinforced with glass fiber–reinforced polymer (GFRP) bars and spirals. The columns were tested under axial loads with variable eccentricities or flexural loading configurations. The test variables included reinforcement type (GFRP and steel), loading type (axial and four-point bending), the ratio of eccentricity-to-column diameter, and the slenderness ratio. Test results revealed that as the eccentricity increased, the peak axial load and the axial and lateral stiffness decreased significantly. Similarly, for the same eccentricity, a reduction in the peak load and both axial and lateral stiffnesses was observed when the slenderness ratio increased. In addition, interaction diagrams for circular GFRP-RC short and slender columns were developed from the experimental results and compared to those obtained analytically. Moreover, a simple modification to account for the slenderness effect on the interaction diagram was proposed. [ABSTRACT FROM AUTHOR]

The complex nonlinear mechanical behavior of the combined system of rock and coal surrounding mine openings is a major obstacle for excavation, stability, and support design in mining thin coal seams. In this paper, the triaxial compression failure characteristics and mechanical response of sandstone–coal (SC) specimens with different combination angles are determined. In addition, the influence of the anchor bolt on the mechanical properties of SC specimens is also considered. The results show that the mechanical parameters of the SC and sandstone–coal–bolt (SCB) specimens are different from those of other intact rocks and are substantially affected by the angle. The peak axial strain and triaxial compressive strength (TCS) of the specimens decreased with increasing angles. To comprehensively analyze the phase mechanical characteristics of the specimens and the differences between them, we also established the crack initiation stress index (CI) and crack damage stress index (CD) to evaluate the specimen fracture process. The established stress indices CI and CD can accurately describe the roles of the bolt and angle of the SC and SCB specimens. The bolt can enhance the mechanical properties of the SC specimen after reaching the peak load, restrain the development of cracks, and ensure that the specimen maintains integrity. It should be noted that this type of SCB system is in line with the long-term stability of roadway support engineering applications. [ABSTRACT FROM AUTHOR]

This article reports the experimental study of the influence of the fiber volume content in steel fiber–reinforced concrete (SFRC) on the acoustic emission (AE) characteristics. Plain concrete and SFRC specimens with various steel fiber contents were tested under unconfined uniaxial compression in the laboratory. Both AE testing and ultrasonic pulse velocity (UPV) methods were used to study the fracture process in the specimens. During the fracture process, the generated AE and axial compressive strain were recorded. The differences in AE characteristics of plain concrete and SFRC specimens were discussed. An absence of a considerable amount of AE for a certain period was observed (silent period of AE) near the peak load for SFRC specimens. The AE-based b-value suddenly decreased near the peak load during the fracture process in plain concrete. However, in the case of SFRC specimens, a sudden decrease near the peak load was not observed, and the b-value decreased gradually until failure, at which point it attained its minimum value. More AE related to shear cracking was observed in the case of SFRC specimens. This was due to interlocking between steel fibers, cement matrix, and coarse aggregates. AE testing is useful for studying the material characterization of SFRC, and is beneficial for assessing damage in structures constructed with SFRC. [ABSTRACT FROM AUTHOR]

Calculation of stresses within a soil body due to surface loading is a required step when designing buried commodities and subgrade wall structures. The Boussinesq equation is commonly used for determining stresses in soil due to surface loading, with examples for use found industrywide. However, the available formulations have limitations, or they only cover simple cases. The purpose of this work is to review the derivation of the Boussinesq equation for vertical and lateral stresses in a soil body and to present several new, closed-form solutions for various surface load cases, including finite line and finite area loads. The formulations are presented as Cartesian coordinate functions such that the stress at any point in the subsurface plane of interest can be found, not just the peak stress or the stress contour at a specific line. This is particularly useful when considering load distribution at a lateral extent from a finite loading, which may be significantly lower than the peak loading. [ABSTRACT FROM AUTHOR]

A dual resonator with electromagnetic transduction was developed to harvest bridge vibration energy at low acceleration and low frequency. The harvester had two cantilever beams: one to carry magnets and the other to carry the coil. The coil was held by the coil holder on the coil-beam in a vertical direction to have a poling direction of magnets perpendicular to it. The device was characterized in-lab and in real bridge environment. In in-lab experimentation at acceleration. In the lab, at acceleration of 0.07 g, the harvester produced 2.7 V voltage and 13 mW power (555 Ω optimal load resistance) output at the first resonant frequency of 3.2 Hz, and output voltage of 3.1 V and 7.8 mW power (at optimal load resistance of 1,200 Ω) at the second resonant frequency of 4.2 Hz. Furthermore, when the voltage was rectified from AC to DC and at 100 kΩ optimal load resistance, 0.5 g acceleration, the output voltage of 19.4 V and power of 3.764 mW was available at 3.2 Hz frequency. A battery was also charged with the DC output of the harvester. Moreover, the real bridge environment characterization tests were made on two prestressed I-section concrete bridges. The harvester on one bridge location produced a peak load voltage of 0.27 V and a peak power of 0.13 mW at resistive load of 555 Ω and 0.024 g peak bridge acceleration. At the second bridge, where the peak acceleration was 0.017 g, the harvester successfully generated a load voltage of 0.32 V and power of 0.18 mW. [ABSTRACT FROM AUTHOR]

Low-temperature cracking is a very common type of distress in flexible pavements in cold areas that extends in the form of longitudinal and transverse cracks on the surface layer. Modifying the properties of the control asphalt cement to improve its performance at low temperatures is a way to control this type of cracking. The effect of using ultrahigh-molecular-weight polyethylene (UHMWPE) as a polymeric additive was investigated with rheological, mechanical, and thermodynamic tests. Bending beam rheometer (BBR) testing of the asphalt cement at low temperatures and mechanical tests, including pull off (PO) and semicircular bend (SCB), were performed on asphalt mixtures to examine the effect of this additive on the low-temperature cracking potential of hot-mix asphalt. In addition, thermodynamic tests, including asphalt cement and aggregate surface free energy (SFE) using the Wilhelmy plate (WP) and the universal sorption device (USD) methods, were performed to better understand the results. Based on the results of the BBR test, the application of UHMWPE improved the performance of the modified asphalt cement at low temperatures. Also, the results of the SFE test showed that using UHMWPE increased the cohesion and the adhesion free energies. These changes were closely correlated with the results of the PO test in cohesive and adhesive modes, respectively. The results of SCB test for parameters including peak load, fracture energy, and fracture toughness demonstrated that the incorporation of UHMWPE significantly improves the low-temperature properties of the modified asphalt mixture. Moreover, based on the statistical analysis, the SFE parameters had a positive effect on peak load and fracture energy. The results for the fracture energy parameter revealed that, after crack formation, only the cohesion free energy parameter was effective on asphalt concrete resistance until the moment of failure. [ABSTRACT FROM AUTHOR]

Large-scale reinforced concrete columns with high-strength reinforcement and concrete were tested. The nominal compressive strength of concrete was 70 MPa. The nominal yield strengths of longitudinal and shear reinforcement were 690 and 790 MPa, respectively. The columns were subjected to double-curvature lateral cyclic loading under constant axial compression. Test variables included the amount of shear reinforcement and level of axial compression. Test results showed that all the nine columns tested failed in shear and showed a successful redistribution of internal forces at diagonal cracking. The stress of shear reinforcement at the peak load increased with an increasing amount of shear reinforcement. Three of four columns with the highest amount of shear reinforcement (0.56%) showed yielding of shear reinforcement at the peak load. By comparing with the test results of 86 high-strength columns from this research and the literature, the minimum shear reinforcement equation of the ACI 318 code was found not able to prevent failure at diagonal cracking and failed to provide a clear trend between the reserve shear strength and the amount of shear reinforcement. A minimum shear reinforcement equation is thus proposed. The equation is based on the Vc equation of the ACI 318 code and can consider the effect of axial compression. Comparing 86 columns shows that the columns that failed at diagonal cracking do not satisfy the proposed equation. Moreover, the proposed equation can provide a clear trend between the reserve shear strength and the amount of shear reinforcement. [ABSTRACT FROM AUTHOR]

Ductility is a desirable trait in an otherwise brittle concrete which is conventionally achieved via methods like introduction of steel reinforcement. While thin spray-on liner (TSL) is a material used in underground support systems to enhance the strength and ductility of rock and shotcrete, its application in concrete is a promising prospect. The study in this paper was conducted to observe the effect of application of Polyurea TSL on the flexural properties of unreinforced and lightly reinforced concrete slabs of varying strengths applied with varying thicknesses of Polyurea. The study used three-point flexural tests on slabs of uniform dimensions, simply supported on all sides, until failure or limit of test setup. Deflection was measured underneath the slab midpoint via a linear displacement sensor. Comparative analysis indicated that for the same strength and steel reinforcement, Polyurea application was significantly associated with an increase in stiffness, peak load, yield load, ductility, and energy dissipation in the specimens. Increasing Polyurea thickness also produced the same trend in the observed parameters. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on the strengthening of rectangular timber beams under monotonic loading. Both flexural and shear behavior of the specimens was studied. A total of five timber beam specimens with identical cross-sections were prepared. The first three specimens had a long span (3 m), whereas the remaining two had a short span (1 m). In order to obtain the benchmark parameters for flexural and shear behavior, one beam specimen from each span group was tested without adopting any strengthening measures. The long beam specimens were tested under four-point loading (for flexure) and the short ones under three-point loading (for shear). One of the long beam specimens was strengthened with mild steel plates bolted on the tension and compression sides. The last long beam specimen was strengthened with a carbon fiber reinforced polymer (CFRP) laminate adequately bonded on the tension side only. The other short beam specimen was strengthened with self-tapping screws in different detailing arrangements on the tension and compression sides to strengthen the specimen against horizontal shear. The performance assessment of all specimens was done on the basis of their peak load resisted, load versus midspan displacement, stiffness response, and failure mode. Last, the theoretical strengths of the specimens were quantified and were compared with the strengths obtained during the tests. It was observed that all strengthening measures adopted improved the targeted flexural and shear performance of the beam specimens. However, the performance improvement achieved was proportional to the cost involved for each strengthening measure adopted. [ABSTRACT FROM AUTHOR]

The main purpose of this research is to assess the influence of different design parameters on the mechanical performance of high-performance fiber-reinforced concrete (HPFRC) mixtures. Special attention is also paid to achieving deflection-hardening behavior in the presence of a large amount of coarse aggregates. Different mixture design parameters were the initial curing ages (3, 7, 28, and 90 days), ratios of Class F fly ash (FA) to portland cement (PC) (0.0, 0.2, and 0.4), addition/type of nanomaterials [nanosilica (NS), nanoalumina (NA), and nanocalcite (NC)], and combinations of fibers [polyvinyl-alcohol + steel (P, S) or brass-coated microsteel + steel (B, S)]. The experimental program included the evaluation of compressive strength, flexural strength, and midspan deflection results in addition to test parameters recorded under biaxial flexural loading via a series of square panel tests, including peak load and energy absorption capacities. Test results revealed that deflection-hardening response coupled with multiple microcracks can be obtained when large amounts of coarse aggregates are available for all HPFRC mixtures. As expected, experimental results change depending on the different curing ages and FA/PC ratios. The most distinctive parameters affecting the results are addition/type of nanomaterials and the presence of different fiber combinations. In the presence of nanomaterials, all results from the different tests improved, especially for NA and NS inclusions. With slight concessions in flexural deflection results, B fiber is shown to be a successful candidate to fully replace costly P fibers because most properties of B, S fiber-reinforced HPFRC mixtures outperformed those with P, S fibers, both under four-point bending and biaxial flexural loading. [ABSTRACT FROM AUTHOR]

This paper describes an experimental investigation on the use of high-strength steel and high-strength concrete to reduce the required reinforcement areas in nuclear shear walls. Two squat rectangular walls with uniformly distributed reinforcement (i.e., without boundary regions) and rectangular penetrations commonly found in nuclear power plant construction were tested under reversed-cyclic lateral loading. Specimen W1 used normal-strength materials and a high reinforcement ratio typical of the state of practice. Specimen W2 had identical dimensions (since nuclear wall lengths and thicknesses are often governed by nonstructural requirements), but used high-strength concrete and significantly reduced areas (by about 50%) of high-strength reinforcement to result in a lateral strength similar to that of Specimen W1. Specimen W2 was able to achieve nearly the same lateral strength (about 90%) as that of Specimen W1 and had slightly greater initial stiffness and diagonal-cracking strength (important design considerations for nuclear walls). As potential limitations, the postcracking stiffness of Specimen W2 was reduced and the wall had wider cracks than Specimen W1 prior to peak load. However, by the attainment of peak load, the crack patterns (i.e., orientation and spacing between diagonal cracks) of the two walls were similar, demonstrating that the reduced reinforcement areas with the same spacing in Specimen W2 did not negatively affect the ultimate load-resisting mechanism. Both walls had shear-dominant failure, but Specimen W2 had a more gradual loss in strength after peak load. Estimations of initial lateral stiffness, diagonal-cracking strength, and peak strength from numerical finite-element analyses were reasonably close; however, the diagonal-cracking strength and peak strength estimates were unconservative (i.e., higher than measured) and need improvement. Needed improvements to existing code design methods and equations for the initial stiffness, diagonal-cracking strength, and peak strength of squat RC walls are also discussed. [ABSTRACT FROM AUTHOR]

In this study, a new hybrid technique for the strengthening of rectangular reinforced concrete (RC) columns under eccentric compressive loading is described, and its effectiveness is assessed experimentally. This technique combines two carbon fiber-reinforced polymer (CFRP) systems for complementary purposes: strips of CFRP wet layup sheets with a certain prestress level using a mechanical device in an attempt to introduce effective concrete confinement, and CFRP laminates applied according to the near surface mounted (NSM) technique to increase the flexural capacity of the RC columns. The effects of the cross section aspect ratio and flexural strengthening ratio of CFRP laminates were investigated in terms of the load carrying capacity of this type of RC columns. All specimens had a height of 1,080 mm, and 3 cross sections were considered, 120 × 120 mm2, 240 × 120 mm2, and 480 × 120 mm2, representing cross section aspect ratios (large/small edge) equal to 1, 2, and 4, respectively. All columns were subjected to eccentric compressive loading until failure. The results show that the new hybrid strengthening technique can enhance the performance of rectangular RC columns in terms of load carrying capacity and ductility under eccentric loading. The cross section aspect ratio played an important role in the confinement effectiveness of the strengthened system. When the cross section aspect ratio increases, the benefits provided by the proposed technique in terms of maximum axial strength and lateral deformability at the peak load of all columns decreased. The load carrying capacity and lateral deformability of the tested RC columns increased with the flexural strengthening ratio. In addition, an analytical model is proposed to evaluate the maximum strength and the axial load–lateral displacement response of rectangular RC columns strengthened according to the newly proposed technique, and a good predictive performance was obtained. [ABSTRACT FROM AUTHOR]

With structural changes in power consumption, peak load demands and peak-valley differences are growing, which motivates peak shaving operations of hydropower systems. A multiobjective mixed-integer nonlinear programming model is presented for short-term hydropower generation scheduling that aims to regulate peak loads and enhance power efficiency. The combined feasible operation zones and the aggregate generation function of each plant are embedded in this model to deal with the operation constraints of units. A set of Pareto solutions of this model is generated by an improved normalized constraint method that narrows the optimization range to ensure the practicality and compact distribution of solutions, each of which represents an aggregated scheduling of cascaded hydropower plants. Then, a mixed integer nonlinear programming formulation is developed to solve the unit commitment problem for each solution, and a fuzzy-based membership value assignment method is employed to extract a best compromise solution for final implementation. A case study of the hydropower plants of the Beipanjiang cascade in China is used to test the proposed approach, verifying its success in generating a practical operating schedule while providing abundant information to decision makers for decision support. [ABSTRACT FROM AUTHOR]

Design of reinforced concrete (RC) bridge members with fiber-reinforced polymer (FRP) bars as internal reinforcement are usually governed by their serviceability parameters, such as crack width and deflection. This study investigates the effect of structural fibers on the shear behavior of RC beams with glass fiber-reinforced polymer (GFRP) rebar as longitudinal reinforcement. The objective of this study is to understand the efficiency of macrosynthetic polyolefin (PO) polymer and a hybrid combination of steel and PO fibers in improving the shear behavior of GFRP-reinforced beams. In total, 13 full-scale RC beams are cast with GFRP rebars as internal reinforcement and varying PO and hybrid fiber dosages. Three different fiber dosages by volume of concrete (vf), namely 0.35%, 0.70%, and 1.0% are considered. The beams are tested under three-point bending configuration with a shear span (a) to effective depth (d) ratio of 2.2 to simulate shear dominant behavior. Experimental results revealed that the addition of fibers increased the postcracking stiffness, peak load, and ductility when compared with control beams with no fibers. Soon after cracking, an excessive load drop in the control specimen is observed due to the low elastic modulus of GFRP rebars. The addition of PO and hybrid fibers reduced the load drop significantly and enhanced the postcracking performance by improving the aggregate interlock and through reduction of residual tensile stresses at the crack tip. The angle of the crack increased with an increase in fiber dosages, indicating the change of the failure mode from brittle shear tension to ductile flexure at higher fiber dosages (0.7% and 1.0%). The shear strength predictions obtained from ACI and RILEM recommendations are found to be very conservative when compared with the test results. [ABSTRACT FROM AUTHOR]

Connections in mass timber structural systems are critical for transferring lateral forces from mass timber elements such as shear walls and diaphragms. Cross-laminated timber (CLT) is a prominent mass timber material used to manufacture these wall and floor assemblies. Although research exists that investigated the fire performance of CLT walls and floors, very little investigation has been devoted to the thermal performance of the connection systems themselves. This void in the data and knowledge surrounding CLT connections is an impediment for modeling the elevated temperature performance of CLT structures. Therefore, a series of shear tests were conducted on a CLT L-bracket connection assembly to characterize the thermal degradation of peak loads and initial stiffness as a function of exposure duration at a given temperature. A total of 116 specimens, including four control specimens, were tested according to a matrix of 28 exposure duration-temperature combinations. Two analytical models are developed to explain the thermal degradation—one assuming a mechanism based on first-order kinetics and the second using a statistical regression. The results of this work indicate that the degradation of peak load and initial stiffness with respect to exposure duration occurred at a linear rate and depended on temperature, according to the Arrhenius activation energy theory. This research is a step toward a holistic evaluation of elevated temperature modeling of CLT structures. [ABSTRACT FROM AUTHOR]

A combined retaining structure (CRS) that consists of numerous piles, a concrete platform, and a gravity retaining wall was built to support a high embankment constructed on a steep slope. In this study, the behavior of an actual CRS was explored to understand bending moment in the pile and lateral earth pressure distribution on the wall with its small lateral displacement and narrow width of retained soil. The internal force and deformation behavior of the CRS were monitored during and after embankment construction. Numerical modeling by FLAC3D was also performed to gain a further understanding of the performance of the CRS. Monitoring and modeling results indicated that the bending moments along piles are reduced effectively by the platform and the retaining wall. The magnitude of earth pressure was larger than that of Coulomb theory. Both the distribution and magnitude of the earth pressure were closely related to the wall displacement and the filling space behind the CRS. Furthermore, seismic behavior of the CRS was investigated. The results showed that the pile segment inside the platform could be damaged under a seismic load with high peak ground acceleration. [ABSTRACT FROM AUTHOR]

This paper discussed the stiffness and cracking behavior of a new kind of reinforcement-stiffened cold-formed U-shaped steel and concrete composite beam (RCUCB) under negative bending. The static behavior of the RCUCB was discussed based on a negative bending experiment of 10 specimens. The reinforcement system consisting of the inverted U-shaped reinforcement, reinforcement truss, and bottom reinforcement was shown to maintain the integral action of the RCUCB, especially after the yield load. The RCUCB was found to behave well in deformability, ductility, and plastic rotation ability under negative bending: (1) the failure deflection and ductility factor reached L0/33 (where L0 is the effective span) and 17.7 respectively; (2) the ductility factor increased with decreasing steel ratio and decreasing reinforcement ratio; and (3) approximately 84.7%–94.0% of the web height yielded at the peak load, resulting in a plastification coefficient of 1.3–1.9. The damage process was defined with the cracking, yielding, and buckling loads approximately equal to 0.16Pu , 0.61Pu , and 0.90Pu , respectively. During the experiment, the degree of shear connection in the negative bending area showed little effect on the negative bending behavior before yield load. Calculation methods for initial stiffness, second stiffness, and cracking moment were proposed, and the calculation results agreed well with the test results. [ABSTRACT FROM AUTHOR]

Estimating the peak value of wind load effects is an important task for engineers of structural and cladding design. Because of the various sources of uncertainties, such as the aerodynamic effect, model selection, and calibration errors, the peak wind load effects may have large variations. This study evaluates the uncertainty of the peak value of wind load effects across multiple samples from a wind tunnel. The Hermite polynomial model (HPM)-based translation process method is adopted to estimate the peak wind load effect. An empirical formula is proposed to estimate the parameters of peak value distribution. Two analytical approaches to model the uncertainty of the peak value at any fractile are proposed based on the probability function and the Gaussianity inference of the peak value. Numerical examples including the wind pressure coefficient and wind-induced response illustrate the performance of the proposed approaches. [ABSTRACT FROM AUTHOR]

Interfacial adhesive bonding of concrete-like materials is strengthened by short Kevlar fibers. The tough and flexible Kevlar fibers, bridging across grain structures, can effectively suppress premature surface and subsurface local fracture at the interface during the formation of fictitious crack. The adhesive joint, formed through either repairing of a gap using epoxy or structural reinforcement using carbon-fibers/epoxy composite, is changed into a composite adhesive joint because of use of Kevlar fibers at the interface. In this study, grey granite samples were tested under three-point-bending with two different interfacial repair conditions: (1) epoxy only, and (2) epoxy with short Kevlar fibers of 6 mm in length. Peak loads and RILEM fracture energy Gf were measured from as-received granite samples, and the two different types of repaired samples. Improvements were observed in both the peak load and fracture energy. Formation of fictitious crack and its influence on the peak load were discussed. [ABSTRACT FROM AUTHOR]