Ugurhan Akyuz

Stress analysis of the human temporomandibular joint

Stress analysis of the human temporomandibular joint (TMJ) consisting of mandibular disc, condyle and fossa-eminence complex during normal sagittal jaw closure was performed using non-linear finite element analysis (FEA). The geometry of the TMJ was obtained from magnetic resonance imaging (MRI). The tissue proportion was measured from a cadaver TMJ. Contact surfaces were defined to represent the interaction between the mandibular disc and the condyle, and between the mandibular disc and the fossa-eminence complex so that finite sliding was allowed between contact bodies. Stresses in the TMJ components (disc, condyle and fossa-eminence complex), and forces in capsular ligaments were obtained. The results demonstrated that, with the given condylar displacement, the stress in the condyle was dominantly compressive and in the fossa-eminence complex was dominantly tensile. The cancellous bone was shielded by the shell shaped cortical bone from the external loading. The results illustrate the stress distributions in the TMJ during a normal jaw closure.

Seismic Resistance Evaluation of Traditional Ottoman Timber-Frame Hımış Houses: Frame Loadings and Material Tests

Traditional Ottoman timber-frame houses (“hımış”) form the major part of the cultural heritage structures in Turkey. There are many studies in the literature regarding the seismic performance of hımış houses, which claim that these structures have an inherent seismically resistant property. However, these studies lack a quantitative engineering approach and are based on observations made after contemporary earthquakes. This study presents the results of the seismic resistance evaluation of traditional Ottoman houses, made by means of reverse cyclic frame tests conducted on six yellow pine and two fir frames with and without infill (brick and adobe) or cladding (bağdadi and şamdolma). The experimental study, which was intended to differentiate the effects of infill materials, frame geometry, and timber type, has revealed that frames with bağdadi cladding and adobe infill resulted in the best and worst structural performances, respectively, while high ductility and good energy dissipation capacity characteristics were determined.

Stability and asymmetric vibrations of pressurized compressible hyperelastic cylindrical shells

Abstract Cylindrical shells of arbitrary wall thickness subjected to uniform radial tensile or compressive dead-load traction are investigated. The material of the shell is assumed to be homogeneous, isotropic, compressible and hyperelastic. The stability of the finitely deformed state and small, free, radial vibrations about this state are investigated using the theory of small deformations superposed on large elastic deformations. The governing equations are solved numerically using both the multiple shooting method and the finite element method. For the finite element method the commercial program ABAQUS is used. 1 The loss of stability occurs when the motions cease to be periodic. The effects of several geometric and material properties on the stress and the deformation fields are investigated.

Tensile Capacities of CFRP Anchors

In reinforced concrete buildings inserting adequate amount of reinforced concrete infills is an effective strengthening technique. Another promising technique is to strengthen the existing hollow clay tile infill with diagonally placed CFRP sheets. In this technique, CFRP sheets are extended to the frame members. The connection between CFRP sheets and frame members is provided by CFRP anchors. If an adequate amount of CFRP anchoring is used, CFRP applied hollow clay tile infill becomes a unique part of the reinforced concrete frame. Thus in this strengthening technique, the effectiveness is dictated by the CFRP anchors. In this study, by means of the prepared test setup, the pull-out strength capacities of CFRP anchors are measured. The effects of concrete compressive strength, anchorage depth, anchorage diameter, and number of fibers on the tensile strength capacity of CFRP anchor are studied.

Analytical Investigation of Lateral Strength of Masonry Infilled RC Frames Retrofitted with CFRP

In this study, two reinforced concrete frames with hollow clay tile masonry infill walls, retrofitted with diagonally applied carbon fiber-reinforced polymer (CFRP), which were tested previously, were analytically investigated. A simple material model for the masonry infill wall strengthened with CFRP is suggested. The lateral strength of each rehabilitated frame was obtained by pushover analysis of four different models using a commercially available finite-element program, and the results were compared with the test results. We also determined the lateral strength of the CFRP-applied masonry infill walls, and compared the results with the results obtained from existing analytical models. Drift capacity of the masonry infill walls strengthened with CFRP was also investigated, and the drift capacity of the masonry infill walls strengthened with diagonally applied CFRP was recommended. It is concluded that the strength of the masonry infilled frames strengthened with diagonally applied CFRP can be satisfactorily predicted with the suggested procedure. The ultimate drift capacity of the masonry infill walls strengthened with diagonally applied CFRP strips was conservatively predicted to be 1.0%.

Forced Vibration Testing and Finite Element Modeling of a Nine-Story Reinforced Concrete Flat Plate-Wall Building

Tunnel form buildings, owing to their higher construction speed and quality, lower cost, and superior earthquake resistance over that of conventional reinforced concrete buildings, have been widely used for mass housing, urban renewal, and post-earthquake reconstruction projects all over the world as well as in Turkey. However, there have been few dynamic tests performed on existing buildings with this structural system. This study investigates the dynamic structural properties of a typical nine-story reinforced concrete flat plate-wall building by forced vibration testing and develops its three-dimensional (3-D) linear elastic finite element structural model. The finite element model that uses the modulus of elasticity for concrete in ACI 318 predicts the natural vibration periods well. Mode shapes are also in good agreement with the test results. Door and window openings in the shear walls, and the basement with peripheral wall emerge as modeling considerations that have the most significant impact on structural system dynamic properties.

Dynamic analyses of isolated structures under bi-directional excitations of near-field ground motions

Nonlinear response history analyses (NRHA) of a 3-story isolated reinforced concrete (RC) building are carried out under both uni- and bi-directional earthquake excitations of near-field records. NRHA are conducted for a wide range of yield strength (Q/W) of lead rubber bearings (LRB), and isolation period (T). Selected near-field records are used to investigate both the contribution of orthogonal components on maximum isolator displacements and accuracy of equivalent lateral force (ELF) procedure on estimation of maximum isolator displacements. Analyses results show that both the contribution of orthogonal components and accuracy of ELF procedure depend on the soil condition where isolation system is implemented.

Lateral Response Comparison of Unbonded Elastomeric Bearings Reinforced with Carbon Fiber Mesh and Steel

The vertical and horizontal stiffness used in design of bearings have been established in the last few decades. At the meantime, applicability of the theoretical approach developed to estimate vertical stiffness of the fiber-reinforced bearings has been verified in different academic studies. The suitability of conventional horizontal stiffness equation developed for elastomeric material, mainly for steel-reinforced elastomeric bearings, has not been tested in detail for use of fiber-reinforced elastomeric bearings. In this research, lateral response of fiber mesh-reinforced elastomeric bearings has been determined through experimental tests and the results have been compared by corresponding values pertaining to the steel-reinforced bearings. Within the test program, eight pairs of fiber mesh-reinforced bearings and eight pairs of steel-reinforced bearings are subjected to different levels of compressive stress and cyclic shear strains. Fiber-reinforced elastomeric bearings may be more favorable to be used in seismic regions due to lower horizontal stiffness that can result in mitigation of seismic forces for levels of 100% shear strain. Damping properties of these types of fiber mesh-reinforced bearings depend mostly on the selection of elastomeric material compounds. Suggestions have been made for the lateral response of fiber-reinforced elastomeric bearings. It has also been determined that the classical equation for lateral stiffness based on linear elastic behavior assumptions developed for elastomeric bearings does not always apply to the fiber-reinforced ones.

Testing and Seismic Capacity Evaluation of a Typical Traditional Ottoman Timber Frame

In Turkey, as well as in Balkan countries, examples of an extant housing tradition namely hımış, which was formed during Ottoman period, can still be observed. In spite of minor local differences according to geographical locations, these Ottoman hımış houses are distinguished with a number of common architectural and technical peculiarities that is worth to preserve. They have similar timber frame construction system with different infill materials. There are numerous reports claiming that the hımış houses are seismically more resistant than other construction types such as reinforced concrete and/or masonry structures. However, nearly all such reports are based on observations made after historical or contemporary earthquakes and lack quantitative engineering approach. For these reasons, within the framework of an ongoing research project, supported by The Scientific and Technological Research Council of Turkey (TUBITAK), coded 106M499, the seismic resistance of traditional timber frame houses in Turkey was investigated. A number of timber frames were tested in the laboratory under cyclic and reverse lateral loading, with and without infill. The results were reproduced with pertinent analytical work. As a result, it was shown that connections that were traditionally made with the sole use of standard nails were always the location of failure. In this paper, the results obtained for one of these frames is presented together with its capacity curve analysis to see whether strengthening is needed or not from seismic design point of view.

A Comparative Study on the Strengthening of RC Frames

In order to improve the behavior of buildings and in order to prevent total collapse, necessary amount of strengthening must be provided. The frame of the test specimen (1/3 scaled, 2-story, 3-bay) is detailed such that it has the common deficiencies of existing buildings in Turkey. Two types of strengthening techniques, namely introducing an infill RC wall, and CFRP strengthened hollow clay tile wall, are investigated. The test specimens are subjected to reversed cyclic quasi-static loading. By means of special transducers, axial force, shear force and bending moment at the base of the exterior columns are measured. Strength, stiffness, and story drifts of the test specimen are determined.