ASSESSMENT OF SHEAR ANALOGY AND TIMOSHENKO METHOD FOR ANALYZING HYBRID CLT UNDER OUT-OF-PLANE LOADING

Timber is a natural material which offers superior mechanical properties in parallel to fiber direction when compared against those in perpendicular to the fibers. Cross-laminated timber (CLT) is made up of layers of structurally graded timber, orthogonally oriented in layers whereby it can sustain loading in both directions. CLT is often used as floor panels, and hence, its performance under out-of-plane loading is of significant interest. Low rolling shear modulus resulting in higher shear flexibility of the cross-layers tend to decrease the effective bending stiffness of CLT sections. Developing hybrid CLT using timbers with higher rolling shear modulus as cross-layers in CLT is considered a viable option to improve its performance under out-of-plane loading. The present study investigates the performance of shear analogy and Timoshenko methods in predicting the deflection of hybrid CLT panels while considering different span-to-depth ratios and various combinations of rolling shear modulus. Numerical models were developed to conduct a parametric study and obtained deflection results were compared against those calculated from the shear analogy method and Timoshenko method. It was observed that for CLT with a small span-to-depth ratio and cross-layers made from material with higher rolling shear modulus, the deflection calculated from the analytical methods deviates from the values obtained from the numerical model.

Evaluating Timoshenko Method for Analyzing CLT under Out-of-Plane Loading

Cross-laminated timber (CLT) is an engineered wood product made up of layers of structurally graded timber, where subsequent layers are oriented orthogonally to each other. In CLT, the layers oriented in transverse direction, generally termed as cross-layer, are subjected to shear in radial–tangential plane, which is commonly known as rolling shear. As the shear modulus of cross-layers is significantly lower than that in other planes, CLT exhibits higher shear deformation under out-of-plane loading in contrast to other engineered wood products such as laminated veneer lumber (LVL) and glue laminated timber (GLT). Several analytical methods such as Timoshenko, modified gamma and shear analogy methods were proposed to account for this excessive shear deformation in CLT. This paper focuses on the effectiveness of Timoshenko method in hybrid CLT, in which hardwood cross-layers are used due to their higher rolling shear modulus. A comprehensive numerical study was conducted and obtained results were carefully analyzed for a range of hybrid combinations. It was observed that Timoshenko method could not accurately predict the shear response of CLTs with hardwood cross layers. Comprehensive parametric analysis was conducted to generate reliable numerical results, which were subsequently used to propose modified design equations for hybrid CLTs.

A Scheduling Method of Cross-Layers Optimization of Polling Weight for AOS Multiplexing

The core mechanism of Advanced Orbit System (AOS) mainly contains the packet channel multiplexing and the virtual channel multiplexing. The multiplexing efficiency and frame time directly affect the performance of the AOS and even the whole system. In this paper, in order to optimize AOS multiplexing performance, a scheduling method of cross-layers optimization of polling weight (CLOPW) is proposed. Different from single sublayer optimization such as the isochronous frame methods, the novel method focuses on factors related to AOS performance of two core sublayers, such as packet distribution, residual function, cache capacity, frame time, and multiplexing efficiency. We build a multiple factors framing model of finite buffer and deduce the formula of packet multiplexing efficiency based on the short correlation. Furthermore, we give the formula for the virtual channel utilization and delay of cross-layer optimization. The experimental results show that the novel scheduling method of cross-layers optimization of polling weight is higher utilization of virtual channel and lower average delay than the isochronous frame method.

ON PERFECTION OF CONSTRUCTIVE AND TECHNOLOGICAL FORMS OF PLATE AND RIBBED TRANSFER STRUCTURES FROM GLUED TIMBER

Introduction. The paper presents the prefabricated whole-glued slab-ribbed superstructures, containing glued beams (fins) and a multi-layered wood-panel from horizontal cross-layers of blank boards, laid successively on glued beams and each other and interconnected by glue seams.Materials and methods. Because of the development of the constructive and technological forms of the considered superstructures, the authors propose the structure composed of plate and ribbed integrally transported prefabricated sections with the width of 3-3.5 m. The authors highlight that the combined action of the detached sections is provided through the nodes of combination on the adjacent ribs of the sections without the complicated compression of all the elements of the superstructure including beams, plates, and diaphragms.Results. The analysis of the stress-deformed span by two methods indicates that both methods determine, with a sufficient degree of accuracy, the nature of the distribution of stresses and strains in sections of the structure. Moreover, the obtained values of the maximum deflections and stresses do not exceed the limit values established by the norms and the corresponding values in a similar construction of the structure with a solid timber slab.Conclusions. The paper shows that the proposed construction with the division of the whole-glued multiridged span structure into separate prefabricated, factory-made sections would significantly expand the usage of laminated wood in bridge construction.

Rolling shear modulus and strength of beech wood laminations

Previous research indicated that the rolling shear properties of European beech wood (Fagus sylvatica) are considerably higher than those of softwood. The aim of the presented investigation was to substantiate previous data on rolling shear modulus and strength of European beech wood and to further evaluate its substitution of softwoods in applications where shear properties are influential, namely as cross layers in cross-laminated timber (CLT). Further, the effect of the annual ring orientation within the boards on shear modulus and strength was of major interest. The beech specimens comprised four different sawing patterns, classified unambiguously with reference to the pith location. The shear properties were determined by 50, two-plate shear tests with specimen cross-section dimensions of 33 mm × 135 mm. A mean rolling shear modulus of 370 N mm-2 was obtained, whereby no significant detrimental effect for pith boards with cracks was observed. In agreement with continuum mechanics, the semi-quarter-sawn boards revealed the highest shear moduli whereas the quarter-sawn boards showed roughly 30% lower values. The mean rolling shear strength was 5.6 N mm-2 for all specimens, whereby pith specimens resulted in generally lower values. The 5% quantile, disregarding pith specimens, was 4.5 N mm-2. In conclusion, the rolling shear strength and modulus exceed the respective characteristic values for softwoods by roughly factors of 5 and 7, indicating great potential for beech wood cross-layers in CLT.

Constraints of nonresponding flows based on cross layers in the networks

In the active queue management (AQM) scheme, core routers cannot manage and constrain user datagram protocol (UDP) data flows by the sliding window control mechanism in the transport layer due to the nonresponsive nature of such traffic flows. However, the UDP traffics occupy a large part of the network service nowadays which brings a great challenge to the stability of the more and more complex networks. To solve the uncontrollable problem, this paper proposes a cross layers random early detection (CLRED) scheme, which can control the nonresponding UDP-like flows rate effectively when congestion occurs in the access point (AP). The CLRED makes use of the MAC frame acknowledgement (ACK) transmitting congestion information to the sources nodes and utilizes the back-off windows of the MAC layer throttling data rate. Consequently, the UDP-like flows data rate can be restrained timely by the sources nodes in order to alleviate congestion in the complex networks. The proposed CLRED can constrain the nonresponsive flows availably and make the communication expedite, so that the network can sustain stable. The simulation results of network simulator-2 (NS2) verify the proposed CLRED scheme.