Ali Awaludin

Load-carrying capacity of steel-to-timber joints with a pretensioned bolt

Previous experimental studies reported that bolt pretensioning greatly increases the initial stiffness and load-carrying capacity of bolted joints. It is also a matter of great importance to structural designers to understand the effect of pretension on the load-carrying capacities of bolted joints, and this study presents an extended yield model that considers the fastener’s pretension force. In the extended yield model, the load-carrying capacity was defined as the load at a slip of 15 mm. The ultimate fastener bending angle at the yielded cross section equivalent to this joint slip, which was affected by the fastener’s axial force, was iteratively evaluated in numerical analyses. The introduction of bolt pretensioning largely increased the joint slip resistance at initial loading, but it decreased the ultimate fastener bending angle. This decrease of fastener bending angle resulted in a relatively low stiffness hardening (or secondary stiffness), which is caused by secondary axial forces associated with embedment of steel plates into the wood member. Prediction was verified by the tests of 36 steel-to-timber joints under three different pretension forces and two loading directions relative to the grain. Some of the observed load-carrying capacities of the joints, particularly in loading perpendicular to the grain, however, were not as high as those expected by the numerical analyses considering the given pretension forces.

Bearing properties of Shorea obtusa beneath a laterally loaded bolt

Empirical equations to determine the bearing strength have been proposed by many researchers and design standards. Because these equations have been developed mainly based on test results of softwood species, it is a matter of great importance (to ASEAN structural engineers) to verify the applicability of these equations for tropical hardwood species, which are commonly used in many ASEAN countries. In this study, wood specimens of Shorea obtusa (a tropical hardwood species) were used and the bearing test under full-hole confi guration was carried out for fi ve different loading angles to the grain. The bearing stress-embedment curve obtained from the test was approximated by a linear elastic-plastic diagram indicating the initial and fi nal stiffness of the curve. Testing showed that the average bearing strength parallel to the grain was 7.25% lower than the prediction given in Eurocode 5. The bearing strength perpendicular to the grain evaluated based on bearing load at initial cracking was substantially different from any predictions given by previous studies or design standards. It was also found that the bearing strength and initial stiffness from the bearing stress-embedment curve for loading at intermediate angles to the grain could be satisfactorily predicted with Hankinson’s formula.

Effects of pretension in bolts on hysteretic responses of moment-carrying timber joints

The adoption of a concept similar to the prestressing technique used in laminated wood decks of bridge structures might increase the initial stiffness or ultimate resistance of dowel-type timber joints by applying pretension to their bolts. This study investigated the effect of pretension in bolts on hysteretic responses and ultimate properties of moment-carrying timber joints with steel side plates. A pretension of 20 kN that yielded a prestress level of 1600 kPa or about 90% of the allowable long-term end-bearing strength of spruce species was applied to the bolts of prestressed joints. The superiority of the prestressed joint over the non-pre-stressed joint was proved by very high hysteretic damping, equivalent viscous damping ratio, and cyclic stiffness. At any given rotation level, hysteretic damping reduction and moment resistance decrement due to continuously reversed loads were found to be small because bolt pretensioning minimized the pinching effect. This study showed that the hysteresis loop of the prestressed joint can be obtained by adding the frictional hysteresis loop due to pretension force into the hysteresis loop of the non-pre-stressed joint. Despite a great increase of initial stiffness, only slight increments in ductility coefficient and ultimate moment resistance were found in the prestressed joint.

One-year stress relaxation of timber joints assembled with pretensioned bolts

In our previous study, great increases of hysteretic damping and initial slip resistance of timber joints were attained by applying axial pretension to the steel fasteners. To evaluate the effectiveness of this method, 1-year stress-relaxation measurement was carried out. Nine prestressed joints were prepared and three of them were restressed after 3 and then 6 months after the initial prestressing. All joints were exposed to indoor conditions, and relaxation of the pretension was regularly measured from time-dependent decreases of axial strain of the bolts. After measurement, the joints were subjected to cyclic and monotonic loading tests until failure. The average ratio of residual stress to the initial prestress after 1 year was about 0.23 and 0.66, respectively, for joints without restressing and those with restressing. A simulated stress-relaxation curve developed from the four-element relaxation model predicted 3% of the initial stress after 5 years. Without a regular restressing program, the initial prestressing effect therefore must be considered negligible. However, about 20% of the pre-stress level can be reasonably assumed if restressing is carried out annually. This small residual stress was found to introduce suffi cient frictional damping to signifi cantly increase the equivalent viscous damping ratio of the joints.

Dynamic response of wall-floor joints of wooden light-frame constructions under forced harmonic vibrations

Shaking table tests of the wall-floor joints of wooden light-frame constructions under forced harmonic vibrations are conducted in this study so as to observe the dynamic responsive characteristics. The principal results are as follows: The responsive characteristics of timber constructions under strong earthquakes cannot be directly correlated with their resonant frequencies under free or forced vibrations with low input accelerations, because they behave as continuous bodies when the input accelerations are less than the apparent frictional limits of structural joints. The apparent frictional limits are reduced by periodic fluctuation of the effective vertical loads as a result of the vertical motion of the specimens. The characteristic dynamic responses of wall-floor joints depend clearly upon the frequency and input accelerations of forced vibrations. These dependencies arise from the nonlinear load-slip relationship of the wall-floor joints. The equivalent stiffness in their successive transient phases decreases as joint slip increases, which gradually changes the resonant frequencies of the wall-floor joints. This indicates that the frequency components dominant to ultimate or safety-limit resistance should be distinguished from those dominant to allowable or serviceability-limit resistance.

Collapse Simulation of Ammu Hawu Traditional Timber House in Nusa Tenggara Timur, Indonesia

Most parts of Indonesia are quite exposed to the risk of major earthquakes, but many traditional timber houses were survived due to earthquake. One of Indonesian traditional timber house is Omo Hada, an indigenous house of Nias people was survived with no damage after the Mw 8.6 Northern Sumatra Earthquake. In Japan, many residential building has been built by using wood material in order to prevent collapse during major earthquake. Wood is considered as one of the most important and reliable construction materials, since it is a renewable and has low weight due to its properties. Collapse mechanism of Ammu Hawu Traditional House with Palm wood (Borassus flabellifer) as main material was analyzed by using Wallstat software and Extended Distinct Element Method (EDEM) as the basis theory. Wallstat is a collapse analysis program which already used in many previous researches to simulate collapse during times of seismic motion. In this study, there are ten models that were analyzed due to El Centro Earthquake 1940, Kobe Earthquake 1995 and Modified El Centro Earthquake 1940, those are, Model 0, 1, 2, 3, 4, 5 up to 11. Model 0 is original model with no reinforcement. In the Model 1, 2, 3, 4, and 5 are the models reinforced with additional vertical shear wall at second story. Model 6, 7, 8, and 9 are the models reinforced with bracing at the first story columns. Whereas in Model 10 is Model 5 which are subjected to modified El Centro Earthquake 1940. The models reinforced with vertical shear walls at second story collapsed and it was found that soft-story occurred due to the El Centro and Kobe Earthquake. It was also found that base shear force values in Model 3 through 5 are higher than the original model, that is, Model 0. Otherwise, Model 6 through 9 survived and the base shear force are smaller than that of Model 0. This bracing reinforcement system showed the effectiveness in preventing earthquake and base shear force to whole structure. Soft-story did not occur in these models. Model 10 also survived due to modified El Centro earthquake. It indicates that the still survive due to local scale earthquake. Moreover, internal force values in all models are higher than the original model. From all those aforementioned parameters, it can be concluded that bracing reinforcement at first story is more effective in preventing structure from collapsing due to earthquake than the models with additional vertical shear walls at second story. Keywords: Ammu Hawu traditional house, Borassus flabellifer, Wallstat software, Extended Distinct Element Method (EDEM), Vertical shear wall, Brace, Collapse mechanism.

Evaluation of bolted connections in wood-plastic composites

Wood-plastic composite (WPC) is a relatively new material that consists of sawdust and plastic polymer using the extrusion process. Due to its attributes such as low water content, low maintenance, UV durability and being fungi and termite resistant. Nowadays, WPC has already been produced in Indonesia using sawdust from local wood such as Albizia (Paraserianthes falcataria) and Teak (Tectona grandis). Moreover preliminary studies about the physical and mechanical WPC board from Albizia sawdust and HDPE plastic have been carried out. Based on these studies, WPC has a high shear strength around 25–30 MPa higher than its original wood shear strength. This paper was a part of the research in evaluating WPC as potential sheathing in a shear wall system. Since still little is known about connection behavior in WPC using Indonesian local wood, this study evaluated the connection for both of these two types of wood-plastic composite. WPC board from Albizia sawdust will be projected as shear wall sheathing and WP...

Structural Condition Assessment of Steel-Framed Maintenance Plant in Muara Badak, Balikpapan, East Kalimantan

Structural condition assessment was conducted to a single-story, steel-framed maintenance plant. The assessment procedure aimed to ensure safe and sound operation of the existing structure, to determine its remaining service life as well as to propose the appropriate remedial actions for the existing structure. The assessment was performed through visual observation, Non-Destructive Testing (NDT), field load testing, also by carrying out structural analysis upon verified structural model. Corrosion and buckling are the main types of deterioration found within the structure owing to high salinity and slender steel sections. Structural analysis gave maximum stress ratio of 0.374. Static load testing resulted in deflection value of 17 mm, while dynamic load testing resulted in dynamic amplification factor of 1.06. In conclusion, the existing structure is considered to be structurally safe and sound with remaining service life of approximately 36 years and subjected to structural maintenance and strengthening.

Experimental and Theoretical Investigation of Bolted Bamboo Joints without Void Filled Material

An experimental and theoretical are presented to calculate the load capacity of shear single connection (SSC) and shear double connection (SDC) without void filled material. The model presents an extension of the Johansen theory for bamboo connection type, also known as the European Yield Model (EYM). The bamboo of Gigantchloa atroviolacea of the most popular as non-wood has been used as a construction material in some region of Indonesia. The uniqueness bamboo is bamboo non-homogen material, sectional shape non-prismatic, the straighthness stems not same, on the culms guiler node and a cross-section in hollow. The diameter of Gigantochloa atroviolacea bamboo used in this study is ranged from 70 to 90 mm. The diameter of bolt is 12.7 mm. The connection strength can be determined with theoretical and eksperimental. Application theory of the European Yield Model could be developed into theory of connection laterally strength of bamboo without void filler material. Factors that affected of connection laterally strength is bamboo thickness, bolt diameter and spesific gravity. The equation four of connection strength base on European Yield model can calculated of according to yield model of accurred. The connection strength is specified from the value smallest of the equation four of connection yield models.