This paper describes how the main purpose of runway pavements is to carry traffic loads conveniently, economically, and safely during its design life. Pavement safety is usually evaluated through several components including skid resistance, rutting susceptibility, light reflectivity of the surface, debris of foreign objects, and area boundary. Pavement slipperiness in terms of skid resistance is the most critical component that affects pavement safety. Adequate runway surface friction is essential in operating the antiskid braking systems installed in most modern aircraft. Lack of skid resistance can cause a serious safety problem if water exists in any form on the runway. The main objective of this paper is to attempt to improve the skid resistance of hot mix asphalt concrete (HMAC) surfaces for airfield pavements without compromising their mechanical properties. In order to achieve this objective, three different airfield mixes were designed using the Marshall mix design method. Sufficient quantity of each mix was fabricated according to the Canadian Specification ASG-06. Test specimens were prepared including slabs and cores. The slabs were tested for their frictional properties using the British pendulum tester, while the core specimens were tested for their indirect tensile strength, moisture sensitivity and shear strength. Test results showed that using coarser aggregates could improve the frictional properties and the mechanical properties of HMAC for airfield pavements. This paper provides details of the testing program and results, and shows the effect of using coarser aggregates to design safer mixes for runways.
Sustainability is now a high priority goal in the construction industry. One way of achieving this aim is to use recycled concrete aggregate (RCA) for base courses and other purposes. However, RCA is not widely used in new concrete mixtures largely because RCA concrete has been reported to be of inferior quality relative to concretes produced with virgin aggregates. In this article, a new mixture proportioning method for RCA concrete is outlined, and it is demonstrated that the method results in RCA concrete mixtures suitable for structural applications, with predictable short- and long-term properties, and requiring less cement than a concrete mixture of comparable quality made with only virgin aggregates.
Various aspects of a general finite‐element program for the nonlinear analysis of steel‐and‐concrete structures is described. The program accounts for the nonlinear behavior of concrete, steel, and shear connectors. Concrete is treated as an orthotropic nonlinear material. The concept of equivalent strain is used to establish independent stress‐strain relationships in the directions of orthotropy. Steel is modeled as an elastoplastic strain‐hardening material, and classical theory of plasticity together with the von Mises failure criterion is applied. For shear connectors, an empirical nonlinear shear force—slip relationship is used. The accuracy and reliability of the program are demonstrated by the analysis of two composite beams and a multigirder bridge over the entire loading range up to failure. The analytical results are compared with the corresponding experimental and/or field data with good agreement between the two. The reported results demonstrate the feasibility and reliability of the nonlinear finite‐element method as an expedient alternative to costly experimental work in some situations.
The interaction between loading plates and supporting structures is very much dependent upon the relative rigidity of the system. This paper first illustrates how an indiscriminate application of the relative rigidity concept can lead to erroneous conclusions in such systems. The paper then applies the concept to explain reported observed failure modes in pipe systems under explosive loads. Numerical studies are presented which simulate the behaviour of square pipe systems under static and explosive loads using the concept of relative rigidity in conjunction with the finite element method. The results of the analysis confirm the hypothesis of the relative rigidity concept. Experimental verification of the theoretical predictions and numerical modelling results are obtained by simulating the explosive failure patterns in simple freezing experiments. The analysis presented in this paper demonstrates the importance of the concept of relative rigidity for explaining certain kinds of observed failure and fracture phenomena. Key words: cracks, explosives, geometric distortion, load transmitting plate, pipes, relative rigidity, soil – foundation interaction, stress waves.
Accurate prediction of corrosion initiation period and service life of reinforced concrete structures requires accurate determination of their chloride diffusion coefficient and binding capacity. Temperature and exposure duration affect these properties, but there is paucity of knowledge regarding the effects of long-term exposure to sub-zero temperatures. Hence, the effects of sub-zero temperature, T, and exposure duration, t, on the chloride diffusion decay index, m, and binding in ordinary Portland cement concrete are investigated. Non-steady natural diffusion tests are conducted at + 5, 0, −5 and −15 °C for 3, 6, 12 and 18 months, and at the end of each period, the total and free chloride concentration profiles are determined. The index m is found to vary over a wide range, it being directly proportional to T and inversely to t. It drastically deviates from the commonly assumed value of 0.2 in the literature. Chloride binding is found to obey the Freundlich isotherm. The coefficient α of the isotherm equals 1.0 ± 0.16 and is only slightly dependent on T or t while its exponent β varies from 0.178 to 0.502, without exhibiting a systematic relationship with either parameter. Binding is noticed to increase with drop in temperature for the first three months of exposure, but over longer exposure durations, no systematic relationship is observed.
Forst-induced soil-pipeline interaction is modelled using a time-dependent thermo-mechanical process. A simplified one-dimensional frost heave model is used to evaluate frost heave, and a beam on elastic foundation finite element is used to model the buried pipeline. The time-dependent creep displacements of frozen soil are determined based on the elastic theory for the multi-layer half space. The frost-related soil stiffness is obtained using an average elastic modulus and treating the freezing soil as a multi-layer half space. The contact pressure exerted on the pipeline by frost heave and by creep effects in the frozen soil is represented by a simple distributed load. A computer program based on the time-dependent finite element method is developed which can be used to calculate frost-induced stresses and deformations of the pipe. A numerical example is presented which demonstrates reasonable agreement between the results from the proposed analysis and available experimental data.
A hybrid reinforcement system is proposed which consists of a low modulus polymeric reinforcement combined with CFRP, and which is believed to overcome the lack of ductility in FRP reinforced concrete members. Three 4.2 m long and 400 mm deep, high strength concrete inverted T-beams were designed using this new concept and were tested under four point bending. Two of the beams contained hybrid reinforcement while the third contained only CFRP reinforcement (control beam). The control beam failed suddenly, following the rupture of the CFRP reinforcement. The beams with hybrid reinforcement failed in a ductile manner at 63% higher load and they had at least three times more deflection at failure than the control beam. In the later beams, deflections substantially increased following the rupture of CFRP, but the moment of resistance of the beams decreased marginally. Upon release of the load, the hybrid reinforced beams rebounded and had very little deflection under self-weight.
No abstract is provided for this article.
Results of an experimental study on the bond performance of deformed steel rebars in concrete made with coarse recycled concrete aggregate (RCA) are presented. The distinctive feature of the study ...
Glass Fiber Reinforced Polymer (GFRP) I-beam-column adhesively bonded connections are tested under combined bending and shear. The special feature of the novel connection is the wrapping of the seat angles at the connection by a carbon fiber reinforced polymer (CFRP) fabric wrap. The wrap is primarily intended to alter the connection failure mode from brittle to pseudo-ductile, thus providing adequate warning of impending failure. Four moment resisting connection configurations are tested, including the reference configuration without the wrap. It is observed that the connection failure is initiated by the fracture of the adhesive, but the provision of the wrap, together with a steel seat angle, alters the failure mode from brittle to pseudo-ductile. The post-peak load deformation is achieved without a large drop in the resistance of the connection. On other hand, the connection with the wrapping and a GFRP seat angle can also change the failure mode to pseudo-ductile, but it could not be done without a large reduction in the connection resistance after the peak load.
A thin‐walled‐box‐girder finite element that can model extension, flexure, torsion, torsional warping, distortion, distortional warping, and shear lag effects was developed using an extended version of Vlasov's thin‐walled beam theory. The element has two end nodes, but it has besides the six nodal degrees of freedom of a conventional beam element, additional degrees of freedom to account for torsional warping, distortion, distortional warping, and shear lag. The governing differential equation pertaining to each action was used to derive the exact shape functions and the stiffness matrix and nodal load vector of the element. An orthogonalization procedure was employed to uncouple the various distortional and shear lag modes. A numerical example was solved that compared the proposed method with the facet‐shell finite element analysis, with good agreement between the two sets of results.
An experimental study is conducted to investigate the shear behaviour and strength of concrete beams made with coarse recycled concrete aggregate. The distinguishing feature of the beams is the manner in which their concrete mixture is proportioned. A new method of concrete mixture proportioning is used wherein recycled concrete aggregate is treated as a two-phase material comprising residual mortar and natural aggregate, and the relative amount and properties of each phase are considered. Using this method, several beams are made of recycled concrete aggregate-concrete and tested to study their serviceability and shear strength. For each beam its load–deflection curve, shear deformations, diagonal cracking load, crack pattern, ultimate shear strength, and failure mode are determined. The results show that the shear performance of reinforced recycled concrete aggregate-concrete beams is comparable, or even superior, to that of beams made entirely with natural aggregates at both the serviceability and ultimate limit states, and the current Canadian Standards Association, American Concrete Institute and Eurocode provisions for shear design can be used without any modification to design recycled concrete aggregate-concrete beams, provided the aforementioned mixture proportioning method is used.
