Insight into the behaviour of bamboo culms subjected to bending

This study describes analytically the behaviour of bamboo culms subjected to bending, and predicts the failure load and stiffness loss after the linear-elastic stage. Basis of the failure load prediction is the identification of the critical failure mechanisms. The study examines analytically four distinct failure mechanisms: Brazier instability, longitudinal tension/compression, tension perpendicular to the fibres and shear parallel to the fibres. It concludes that, for the three bamboo species examined (Moso, Guadua and Kao Jue), critical failure mechanisms are tension perpendicular to the fibres (with potential tension-shear interaction) and longitudinal compression. Which of the two mechanisms occurs first depends on the case-specific material properties and culm radius-to-thickness ratio. Regarding stiffness loss, the main cause is longitudinal splitting. The extent of the stiffness loss depends on crack length, crack number and crack location along the culm circumference. Secondary causes are nonlinear geometric effects at the large deflection stage. Assuming a parabolic deformed shape, a single equation can describe the stiffness loss induced by nonlinear geometric effects, regardless of material properties and culm geometry. Comparing the analytical results with pertinent experimental data, the proposed equations are sufficiently accurate in their prediction of failure load and stiffness loss, although they tend to underestimate both

Chattering: an overlooked peculiarity of rocking motion

Complete chattering occurs when a structure undergoes a theoretically infinite sequence of impacts in finite time, that eventually bring the structure to the state of persistent (continuous) contact. This study investigates the conditions under which a rigid rocking block undergoes complete chattering when subjected to sinusoidal ground excitation. The analysis explains how the acceleration amplitude of the ground excitation affects the chattering time. It also proves that there exists a (sinusoidal) ground acceleration amplitude, below which rocking motion terminates even under a nonzero ground excitation, almost independently of the frequency of the ground excitation. Furthermore, the study adopts perturbation theory and proposes an asymptotic approximation of the time needed for chattering to be completed, i.e. chattering time. It then verifies the asymptotic approximation using an independent semi-analytical approach. Overall, the results highlight the importance of complete chattering on the dynamic rocking response; a feature of nonlinear dynamics which is often overlooked in earthquake engineering.This study has been funded by the STAND4-HERITAGE project (new STANDards FOR seismic assessment of built cultural HERITAGE) that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant No. 833123) as an Advanced Grant. Its support is gratefully acknowledged. The opinions and conclusions presented in this paper are those of the authors and do not necessarily reflect the views of the sponsoring organization

Engineering Structures Seismic response analysis of skew bridges with pounding deck-abutment joints

a b s t r a c t In this paper the seismic response of short skew bridges with deck-abutment pounding joints is revisited. The permanent deck rotations and transverse displacements of such bridges after the recent earthquake in Chile created an incentive to revisit their non-conventional behaviour. A novel non-smooth rigid body approach is proposed to analyze the seismic response of pounding skew bridges which involves oblique frictional multi-contact phenomena. The coupling of the response, due to contact, is analysed in depth. It is shown that the tendency of skew bridges to exhibit transverse displacements and/or rotate (and hence unseat) after deck-abutment collisions is not a factor of the skew angle alone, but rather of the plan geometry plus friction. This is expressed with proposed dimensionless criteria. The study also unveils that the coupling is more pronounced in the low range of the frequency spectrum (short-period excitations/flexible structures) and presents novel dimensionless response spectra for the transverse displacements and rotations, triggered by oblique contact in a skew bridge subsystem. Despite the complexity of the response, the proposed spectra highlight a clear pattern. The dimensionless rotations, arising from contact, decline as the ratio of the structural versus excitation frequency increases and become practically negligible in the upper range of the frequency spectrum. Finally, a pilot application to a typical skew bridge is presented

Effect of a longitudinal crack on the flexural performance of bamboo culms

Splitting parallel to the culm fibers is common in full-culm bamboo structural members, even early in a structure’s lifespan. Currently, there is insufficient knowledge on the effect of splitting on member performance, which induces significant uncertainties in bamboo member engineering design. This is a potential threat to the safety of existing and future full-culm bamboo structures. This study investigates analytically the effect of a longitudinal crack on the stiffness of an originally intact bamboo culm in flexure. The study develops analytical expressions that describe stiffness loss in two flexure cases (a three-point bending and a four-point bending test) and verifies them with available experimental results and numerical simulations. Main cause of the stiffness loss is torsion-induced deflections, with secondary cause being shear deformations. Importantly, stiffness loss solely depends on two dimensionless parameters: the shape factor (radius-to-thickness ratio) and a factor that is a function of material properties and ratio of shear span length to culm diameter. Additionally, the study proves analytically that friction at the load application points mitigates torsion-induced deflections. This has important implications for bamboo structure design and testing standards, indicating that the manner in which loads are transferred on beams affects the apparent beam stiffness when a crack appears

Exploring perceptions on participatory management of NATURA 2000 forest sites in Greece

Several studies in the biodiversity management literature investigate the potential shift from state-based forest management to participatory management frameworks. A main challenge in this context is to identify social factors influencing the level of public acceptability towards co-management frameworks especially in countries where the state has had traditionally a very strong role in the management of natural resources. The present paper aims to investigate the social factors influencing the level of acceptability for participatory management frameworks in two forest protected areas of Greece differing in the date of their establishment: the Tzoumerka–Peristeri–Arachthos Gorge National Park and the Vikos–Aoos National Park. Specifically, through the distribution of a structured questionnaire to local communities, we explored the influence of social factors (trust in institutions, social trust and social networks) on citizens' perceptions for a shift in participatory management frameworks. Furthermore, we explore the restriction that citizens perceive from the implementation of such frameworks. According to the study, there is clear preference towards a collaborative management framework which is based on the cooperation of local communities with state actors. Social trust, social networks and institutional trust have a significant impact on citizens' perceptions, especially for collaborative management policies which promote the cooperation of local communities with public actors. Finally, the level of restriction that citizens perceive from each proposed policy is also linked with the level of acceptability

Exploring perceptions on participatory management of NATURA 2000 forest sites in Greece

Several studies in the biodiversity management literature investigate the potential shift from state-based forest management to participatory management frameworks. A main challenge in this context is to identify social factors influencing the level of public acceptability towards co-management frameworks especially in countries where the state has had traditionally a very strong role in the management of natural resources. The present paper aims to investigate the social factors influencing the level of acceptability for participatory management frameworks in two forest protected areas of Greece differing in the date of their establishment: the Tzoumerka–Peristeri–Arachthos Gorge National Park and the Vikos–Aoos National Park. Specifically, through the distribution of a structured questionnaire to local communities, we explored the influence of social factors (trust in institutions, social trust and social networks) on citizens' perceptions for a shift in participatory management frameworks. Furthermore, we explore the restriction that citizens perceive from the implementation of such frameworks. According to the study, there is clear preference towards a collaborative management framework which is based on the cooperation of local communities with state actors. Social trust, social networks and institutional trust have a significant impact on citizens' perceptions, especially for collaborative management policies which promote the cooperation of local communities with public actors. Finally, the level of restriction that citizens perceive from each proposed policy is also linked with the level of acceptability

A semi-analytical approach to approximate chattering time of rocking structures

This paper investigates the seismic behaviour of a freestanding rigid rocking block when subjected to low amplitude sinusoidal ground excitations. An important scenario in such cases is the complete chattering the block might exhibit. Complete chattering occurs when the block undergoes a theoretically infinite sequence of decaying impacts that converge to the state of persistent (continuous) contact in finite time, even under a nonzero ground excitation. This study proposes a semi-analytical approach that approximates the (finite) time required for this to happen, i.e. chattering time. Specifically, this paper provides a detailed description of the semi-analytical scheme and shows the influence of the amplitude of the ground acceleration on the approximation of the chattering time. Importantly, the proposed scheme is based on the realisation that, during chattering, and after a sufficiently large number of impacts, the ratio of the time-intervals of every two consecutive impacts becomes constant and equal to the square of the coefficient of restitution. The proposed semi-analytical approach efficiently approximates chattering time providing a state-of-the-art mathematical formulation of the chattering phenomenon for the rocking problem.- (undefined

Characterizing the performance of transversely confined multi-culm bamboo to steel connections

The present research experimentally examines the axial behavior of transversely confined multi-culm bamboo to steel connections, using Kao Jue (Bambusa pervariabilis) bamboo species. The study characterizes under axial monotonic loading, the performance in terms of strength, ductility and failure modes. It then evaluates changes in performance under axial quasi-static reversed cyclic loading. Findings reveal that transverse confinement (through hose-clamps) is highly effective in preventing longitudinal splitting of bamboo culms. The connections exhibit large plastic deformations with sufficient strength and ductility. When compared to the monotonic response, early bolt-fracture hinders the cyclic performance. The connections nevertheless comply with the philosophy of capacity-based design — the ductile components (i.e. the bolts) fail before the brittle components (i.e. the culms). Notably, the adopted European Yield Model can analytically estimate the experimental yield loads with good accuracy. This ultimately indicates a path towards a more rational and engineered design of bamboo structures