Showing papers on "Flexural strength published in 1994"
TL;DR: In this article, a simple method is proposed whereby the strength enhancement provided by axial compression is separated from the concrete component of shear strength and considered to result from arch action.
Abstract: Aspects relating to the shear strength of circular and rectangular columns under seismic loading are presented An examination of existing design equations reveals wide differences in predicted responses Particular emphasis is placed on models capable of representing the interaction between flexural ductility and shear strength A simple method is proposed whereby the strength enhancement provided by axial compression is separated from the concrete component of shear strength and considered to result from arch action The strength of the concrete component is reduced as flexural displacement ductility increases Prediction of shear strength from the proposed and alternative methods are compared with results from a wide range of tests of columns failing in shear The proposed method is shown to provide significantly improved correlation with experimental results Conservative modifications are made to enable the method to be used for design
515 citations
TL;DR: In this article, a new technique for seismic strengthening of concrete columns is presented, which requires wrapping thin, flexible high-strength fiber composite straps around the column to improve the column's ductility and strength.
Abstract: Bridge failures in recent earthquakes such as the 1989 Loma Prieta earthquake have attracted the attention of the bridge engineering community to the large number of bridges with substandard seismic design details. Many concrete columns in bridges designed before the new seismic design provisions were adopted have low flexural ductility, low shear strength, and inadequate lap length for starter bars. These problems, compounded by flaws in the design of structural systems, have contributed to the catastrophic bridge failures in recent earthquakes. In this paper, a new technique for seismic strengthening of concrete columns is presented. The technique requires wrapping thin, flexible high-strength fiber composite straps around the column to improve the confinement and, thereby, its ductility and strength. Analytical models are presented that quantify the gain in strength and ductility of concrete columns externally confined by means of high-strength fiber composite straps. A parametric study is conducted to examine the effects of various design parameters such as concrete compressive strength, thickness and spacing of straps, and type of strap. The results indicate that the strength and ductility of concrete columns can be significantly increased by wrapping high-strength fiber composite straps around the columns.
484 citations
447 citations
TL;DR: In this paper, the authors evaluated the mechanical properties of a kaolinite/fiber soil composite by a series of laboratory unconfined compression, splitting tensile strength, three-point bending, and hydraulic conductivity tests.
Abstract: The mechanical properties of a kaolinite/fiber soil composite were evaluated by a series of laboratory unconfined‐compression, splitting‐tension, three‐point‐bending, and hydraulic‐conductivity tests. The inclusion of randomly distributed fibers significantly increased the peak compressive strength, ductility, splitting tensile strength, and flexural toughness of kaolinite clay. The increase in strength and toughness was a function of fiber length and content, and the water content of the composite. Increasing fiber content increased the compressive and tensile strength, and the toughness index of kaolinite clay, with the effect being more pronounced at lower water contents. The contribution of fibers to peak compressive and tensile strengths were reduced, and ductility increased, with increasing fiber length. The fiber inclusion increased the hydraulic conductivity of the composite and the increase was more pronounced at higher fiber contents. Despite the increase, the hydraulic conductivity of the compo...
391 citations
TL;DR: In this paper, reinforced concrete (RC) beams are initially loaded to 85% of the ultimate flexural capacity and subsequently repaired with FRP (fiber reinforced plastic) plates, bonded to the soffit of the beam.
Abstract: In this study, the reinforced concrete (RC) beams are initially loaded to 85% of the ultimate flexural capacity and subsequently repaired with FRP (fiber reinforced plastic) plates, bonded to the soffit of the beam The plate thickness is varied to assess the premature failure initiated at the plate curtailment zone due to the high concentration of shear and peeling stresses Different repair and anchoring schemes were conducted in an effort to eliminate such failures and insure ductile behavior The results indicated that the flexural strength of the repaired beams is increased The ductile behavior of the repaired beams is inversely proportional to the plate thickness The use of an I-jacket plate provided a proper anchorage system and improved the ductility of beams repaired with plates of large thickness
319 citations
TL;DR: In this paper, the effect of void content on the static strength and fatigue life of composite laminates under flexural loading was investigated. And the authors proposed a fracture criterion correlating the ultrasonic attenuation to the strength of composite laminate and showed that voids have a strong detrimental effect on the fatigue life.
255 citations
TL;DR: In this article, a theoretical and experimental investigation conducted to study the shear failure mode of reinforced concrete bridge columns designed before 1971, and to establish the effectiveness of full-height steel jackets for enhancing the seismic shear strength is described.
Abstract: A theoretical and experimental investigation conducted to study the shear failure mode of reinforced concrete bridge columns designed before 1971, and to establish the effectiveness of full-height steel jackets for enhancing the seismic shear strength is described. In this first part of a two-part paper, theoretical considerations relating to assessing the shear strength of existing columns of circular or rectangular sections are presented. Current design approaches are compared with more recently developed, and less conservative, predictive methods. Models are presented for predicting the enhancement to shear strength provided by circular or elliptical (for rectangular section) jackets. Design details of an experimental test program to determine "as-built" and retrofitted column shear strength are presented.
213 citations
TL;DR: In this paper, the authors used three independent jacks orthogonally disposed, making it possible to apply a purely tensile force, so that the secondary flexural stresses, if kept under control, constitute a degree of error comparable with the values allowed for normal testing apparatus.
Abstract: Tests were carried out using three independent jacks orthogonally disposed, making it possible to apply a purely tensile force, so that the secondary flexural stresses, if kept under control, constitute a degree of error comparable with the values allowed for normal testing apparatus. The method enables a stress versus strain curve to be plotted with the descending (softening) branch up to the point where the cross-section of the tensile specimen breaks away. The principal purpose is to avoid any spurious effect that might provide a fallacious explanation of the recurring size effects on apparent tensile strength and fictitious fracture energy. Once the secondary effects have been excluded, only the disorder and fractality of the concrete microstructure remain to explain such fundamental trends. In the case of tensile strength, the dimensional decrement represents self-similar weakening of the material ligament, due to pores, voids, defects, cracks, aggregates, inclusions, etc. Analogously, in the case of fracture energy, the dimensional increment represents self-similar tortuosity of the fracture surface, as well as self-similar overlapping and distribution of microcracks in the direction orthogonal to that of the forming macrocrack.
194 citations
TL;DR: In this paper, a series of reinforced concrete beams were tested in four-point bending to determine the ability of externally bonded composite fabrics to improve the beams' flexural capacity and stiffness.
187 citations
TL;DR: In this paper, the flexural behavior of a strain-hardening engineered cementitious composite (ECC) is studied and compared with that observed in a regular fiber/reinforced CPM.
Abstract: In this paper the flexural behavior of a strain-hardening engineered cementitious composite (ECC) is studied and compared with that observed in a regular fiber/reinforced cementitious composite (FRC). Unlike concrete or regular FRC, ECC materials are characterized by their ability to sustain higher levels of loading after first cracking while undergoing additional straining. This strain-hardening behavior gives ECCs a significant advantage under flexural loading. In quasi-brittle materials such as regular FRC, the ratio of flexural strength (the modulus of rupture) to tensile strength is known to vary between 1 and 3, depending on the details of the reinforcement and the geometry of the specimen. In this paper, the strain-hardening behavior observed in an ECC led to a high flexural-strength-to-tensile-strength ratio. In a third-point bending test, the flexural strength of an ECC was measured to be five times its tensile (first-cracking) strength. This result was also predicted by a simple theoretical model. The model can be used for the purpose of optimizing the flexural strength of ECCs.
TL;DR: With the exception of Young's modulus, all mechanical properties of the tested materials were significantly improved when a silanized hydroxyapatite filler had been used.
TL;DR: In this paper, the measured flexural strength of freshwater ice and sea ice have been compiled with a view towards correlating the measured results, and the results indicate a very good correlation (r2= 0.77) between the flexural strengths (σf) and the brine volume (νb) with a functional form σf = 1.76 e−5.
TL;DR: In this article, the properties of SiC composites reinforced with Nicalon have been investigated and a lowoxygen-content SiC fiber referred to as Hi-Nicalon has been developed for ultra-high temperature use.
TL;DR: In this article, an epoxy resin was cured while in intimate contact with small amounts of epoxy-pharmic montmorillonites, and it was determined that cured epoxy exists within the Montmorillonite interlayer by the observation of very high interlayer spacings, even greater than 8 nm.
Abstract: An epoxy resin was cured while in intimate contact with small amounts of epoxyphilic montmorillonites. It was determined that cured epoxy exists within the montmorillonite interlayer by the observation of very high interlayer spacings, even greater than 8 nm, Generally, epoxy compounds containing montmorillonites that had been swollen in the curing agent prior to curing exhibited larger interlayer spacings, especially among the non-dispersed montmorillonite layers. The maximum observed residual stress was reduced by greater than 50% in the epoxyphilic montmorillonite/epoxy compounds over that of the pure epoxy. The epoxyphilic montmorillonite/epoxy compounds generally exhibited higher values of glass transition temperature, flexural modulus, and ultimate flexural strength than the pure epoxy. The tyramine-montmorillonite compounds typically had the highest values overall.
TL;DR: The results show that the mechanical properties of the tested materials are in some cases affected by long-term aging in water.
TL;DR: In this paper, the electrical, mechanical and thermal properties of 8 mol% yttria-stabilized zirconia (8YSZ) and alumina composites have been examined as a function of the alumina content.
TL;DR: In this article, a two-dimensional spectral estimator based on the maximum entropy method was used to map the spatial variation of flexural rigidity along the Basin and Range transition to the Colorado Plateau and Middle Rocky Mountains physiographic provinces.
Abstract: Stochastic inversion for flexural loads and flexural rigidity of the continental elastic layer can be accomplished most effectively by using the coherence of gravity and topography. However, the spatial resolution of coherence analysis has been limited by use of two-dimensional periodogram spectra from very large (greater than 10(exp 5)sq km) windows that generally include multiple tectonic features. Using a two-dimensional spectral estimator based on the maximum entropy method, the spatial resolution of flexural proerties can be enhanced by a factor of 4 or more, enabling more detailed analysis at the scale of individual tectonic features. This new approach is used to map the spatial variation of flexural rigidity along the Basin and Range transition to the Colorado Plateau and Middle Rocky Mountains physiographic provinces. Large variations in flexural isostatic responses are found, with rigidities ranging from as low as 8.7 x 10(exp 20) N m (elastic thickness (T(sub e) = 4.6 km) in the Basin and Range to as high as 4.1 x 10(exp 24) N m T(sub e) = 77 km) in the Middle Rocky Mountains. These results compare favorably woith independent determinations of flexural rigidity in the region. Areas of low flexural rigidity correlate strongly with areas of high surface heat flow, as is expected from the contingence of flexural rigidity on a temperature-dependent flow law. Also, late Cenozoic normal faults with large displacements are found primarily in area of low flexural rigidity region. The highest flexural rigidity is found within the Archean Wyoming craton, where evidence suggests that deeply rooted cratonic lithosphere may play a role in determining the distribution of tectonism at the surface.
TL;DR: In this article, a perturbation method of solution is proposed to calculate changes in the modal dispersion curves caused by the differences in elastic constants between the anisotropic formation of interest and a reference, or unperturbed, isotropic formation.
Abstract: A perturbation method of solution is an efficient way of analyzing elastic wave propagation along a borehole in anisotropic formations. The perturbation model allows us to calculate changes in the modal dispersion curves caused by the differences in elastic constants between the anisotropic formation of interest and a reference, or unperturbed, isotropic formation. The equivalent isotropic constants in the reference formation are obtained from the appropriate compressional‐and shear‐wave velocities for the selected propagation and polarization directions of the flexural mode. This choice of the unperturbed solution means that the required perturbation is minimal, resulting in enhanced accuracy of the perturbed solution. Computational results are presented for the dispersion curves of borehole flexural waves in a transversely isotropic (TI) formation as a function of borehole deviation from the TI symmetry axis. In addition, radial distributions of displacement and stress fields associated with the flexura...
TL;DR: In this article, the authors derived stress-strain relationships for compressed concrete confined by various quantities and arrangements of transverse reinforcement to derive design charge, and refined design equations to determine the quantities of transversal reinforcement required for specified curvature-ductility levels.
Abstract: Previously derived stress-strain relationships for compressed concrete confined by various quantities and arrangements of transverse reinforcement are used in cyclic moment-curvature analyses of a range of reinforced concrete columns to derive design charge. The design charts permit the enhanced flexural strength of confined columns to be obtained. They also permit the quantities of transverse reinforcement required to achieve particular curvature-ductility factors in the potential plastic-hinge regions of reinforced concrete columns to be determined. The column section is considered to have reached its available ultimate curvature when either the moment resisted has reduced to 80% of the ideal flexural strength, or the strain energy absorbed in the transverse reinforcement has reached its strain energy absorption capacity, or when the longitudinal steel has reached its limiting tensile or compressive strain, whichever occurs first. Refined design equations to determine the quantities of transverse reinforcement required for specified ductility levels are derived on the basis of the design charts. The equations are an improvement on the current provisions of concrete design codes.
TL;DR: In this article, two series of composite precast concrete sandwich panel (PCSP) systems containing various connector reinforcement and construction details were tested in flexure and fatigue testing indicated relatively minor stiffness loss over 55,000 loading cycles.
Abstract: Two series of composite precast concrete sandwich panel (PCSP) systems containing various connector reinforcement and construction details were tested in flexure. Panels of one series utilized details similar to certain commercially produced panels, while the second series panels contained modified details to better evaluate interface shear transfer behavior. Results of static testing indicated that a high degree of composite stiffness and composite flexural capacity can be attained with truss girder connectors oriented longitudinally in the panels. Test results also showed that construction details can have a significant impact on the distribution of shear in elements crossing the interface. Results of fatigue testing indicated relatively minor stiffness loss over 55,000 loading cycles.
TL;DR: In this article, simulated seismic load tests on 11 reinforced concrete columns are described and the authors check an analytical approach for the determination of the available flexural ductility and the enhancement of flexural strength of columns with various levels of transverse confining reinforcement.
Abstract: Simulated seismic load tests conducted on 11 reinforced concrete columns are described. The columns had a 400-mm (15.7-in.) square or octagonal cross section and contained various quantities of transverse reinforcement. The columns were subjected to either low, moderate, or high axial compressive loads and to reversible quasi-static lateral loads that simulated severe earthquake loading. The tests were conducted to check an analytical approach for the determination of the available flexural ductility and the enhancement of flexural strength of columns with various levels of transverse confining reinforcement. The analytical approach for determining the quantities of transverse reinforcement required for confinement is shown to be conservative and to lead to equations more suitable for the design of transverse reinforcement for confinement than current code equations. Conclusions are also reached concerning the required length of the confined region in the potential plastic-hinge zones of reinforced concrete columns.
TL;DR: In this paper, the effects of thermal treatments and of a sintering additive (Na3PO4) on the microstructure, flexural strength and fracture toughness were investigated.
Abstract: Polycrystalline hydroxyapatite (HAP) ceramics were densified by hot pressing. The effects of thermal treatments and of a sintering additive (Na3PO4) on the microstructure, flexural strength and fracture toughness were investigated. Hot pressing without additive resulted in dense HAP having a small average grain size (below 0.5 μm). Spontaneous microcracking of the material was also noted. This originated from the thermal expansion anisotropy of HAP crystals. The presence of the sintering aid promotes grain growth. Dense materials exhibited mechanical properties depending on the microstructure. The highest values obtained were 137 MPa and 1.2 MPa % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaWaaOaaaeaaci% GGTbaaleqaaaaa!36FA!\[\sqrt \operatorname{m} \] for the flexural strength and fracture toughness, respectively. A decrease of both strength and toughness was observed with increasing average grain size. This behaviour is attributed to the weakening of the grain boundaries by either the development of initial microcracking or the Na3PO4 addition. It is concluded that hot pressing is very useful to elaborate dense HAP having good mechanical characteristics.
TL;DR: In this article, an experimental investigation was conducted to investigate the behavior of composite columns subjected to simulated seismic loading conditions, and the results of the test program indicate that encased composite columns possess exceptional cyclic strength and ductility if buckling of the longitudinal reinforcement is inhibited.
Abstract: An experimental investigation was conducted to investigate the behavior of composite columns subjected to simulated seismic loading conditions. Eight two‐thirds‐scale specimens were tested, each consisting of a structural steel shape encased in reinforced concrete. The parameters studied in the test program included the degree of concrete confinement required to achieve adequate ductility under cyclic loading, effectiveness of flange shear studs for enhancing flexural stiffness and strength, concrete compressive strength, and the shear resistance mechanism of the composite column. The results of the test program indicate that encased composite columns possess exceptional cyclic strength and ductility if buckling of the longitudinal reinforcement is inhibited. The encased steel shape was found to provide the primary resistance to transverse shear during overloading, with the shear studs not effective in enhancing the flexural resistance to lateral loading. The specimen flexural capacity under combined axia...
TL;DR: In this article, the basic elasticity relationship for unidirectional composites, together with the Adams-Bacon damping criterion, are used for prediction of moduli and flexural damping of anisotropic CFRP and GRP beams with respect to fiber orientation.
TL;DR: In this paper, the contribution of the concrete to the flexural capacity of concrete-filled hollow structural sections is acknowledged as an alternative approach, but no method of a method of calculating the capacity of a hollow structural section is presented.
Abstract: In Standard CAN/CSA S16.1-M89, the contribution of the concrete to the flexural capacity of concrete-filled hollow structural sections is acknowledged as an alternative approach, but no method of a...
TL;DR: In this article, the critical mode I stress-intensity factor, the critical J integral, and the tensile strength can be determined simultaneously from a single ring-test specimen using bending tests.
Abstract: Testing procedures and methods of analysis for determining the fracture toughness of soils using the ring test are described and values of fracture toughness measured for 132 compacted specimens of two cohesive soils are presented. The critical mode I stress‐intensity factor, the critical J integral, and the tensile strength can be determined simultaneously from a single ring‐test specimen. The critical J integral was approximately equal to the energy‐release rate computed from the critical mode I stress‐intensity factor measured for the same specimen. A strong correlation between fracture toughness and ring‐specimen tensile strength was found. Effects of material type, water content, soil‐placement conditions, rate of loading, and specimen size have been studied, and values of fracture toughness measured by bending tests are compared to ring‐test results. Test results show that fracture toughness of cohesive soils is affected significantly by material type and water content at time of fracture. In contra...
TL;DR: The use of a bonding agent improves the bond strength of porcelain-fused-to-milled titanium and cast high palladium/conventional porcelains.
TL;DR: In this paper, the authors measured the mechanical properties of pressureless sintered SiC with Al2O3 addition and attributed the increase in fracture toughness and strength to the presence of a liquid phase which results in the formation of platelets of an α-SiC.
Abstract: Mechanical properties of pressureless sintered SiC with Al2O3 addition were measured. The increase in fracture toughness and strength is attributed to the presence of a liquid phase which results in the formation of platelets of an α-SiC. The highest values for flexural strength and toughness were measured on samples with ∼ 10 wt% Al2O3 addition. Pull out, crack bridging and crack deflection are identified as the major strengthening and toughening mechanisms.
TL;DR: In this article, the loading rate and temperature dependence on flexural fatigue behavior of satin woven CFRP laminates consisting of a matrix resin with a high glass transition temperature is investigated.
Abstract: Generally, the mechanical behavior of polymer resins depends remarkably on time and temperature, which is called viscoelastic behavior. Thus, it can be presumed that the mechanical behavior of a CFRP using polymer resins is also time and temperature dependent. In this paper, the loading rate and temperature dependence on flexural fatigue behavior of satin woven CFRP laminates consisting of a matrix resin with a high glass transition temperature is investigated. The results show that not only flexural static strength but also flexural fatigue strength of the CFRP laminate depends on time and temperature even at temperatures that are much lower than the glass transition temperature. The reciprocation law of time and temperature was found to be applicable for both the flexural static and fatigue strengths. The fatigue and static fracture modes were found to be similar for the wide ranges of time and temperatures tested. The slope of the S-N curves also remains the same despite the large temperature range and...