Ahmad Baharuddin Abd. Rahman

The distribution of labdane diterpenes in the zingiberaceae of Malaysia

Labda-8(17),12-diene-15,16-dial and coronarin E were isolated from the chloroform extract of the rhizomes of Alpinia javanica. The structures were elucidated spectroscopically. This is the first report of the isolation of coronarin E from Alpinia species. The distribution of these two labdane diterpenes within the Zingiberaceae is reported

Real-time Seismic Damage Detection of Concrete Shear Walls Using Artificial Neural Networks

Concrete shear walls are widely employed in buildings as a main resistance system against lateral loads. Early identification of seismic damage to concrete shear walls is vital for deciding post-earthquake occupancy in these structures. In this article, a method based on artificial neural networks for real-time identification of seismic damage to concrete shear walls was proposed. Inter-story drifts and plastic hinge rotation of concrete walls were used as the inputs and outputs of a MLP neural network. Modal Pushover Analysis was employed to prepare well-distributed data sets for training the neural network. The proposed method was applied to a five-story concrete shear wall building. The results from the network were compared with those obtained from Nonlinear Time History Analysis. It was observed that the trained neural network successfully detected damage to concrete shear walls and accurately estimated the severity of seismic-induced damage.

A wavelet-based technique for damage quantification via mode shape decomposition

In this study, a neuro-wavelet technique was proposed for damage identification of cantilever structure. At first, damage localisation was accomplished through mode shape decomposition using discrete wavelet transforms. Subsequently, a damage indicator was defined based on the detail coefficients of the decomposed signals. It was found that distinct patterns relate the damage indicators to damage locations. Considering this property, a neural network ensemble was developed for damage quantification. Damage indicators and damage locations were selected as input parameters for the neural networks. Three individual neural networks were trained by input samples obtained from different combinations of decomposed mode shapes. Then, the outcomes of the individual neural networks were fed to the ensemble neural network for damage quantification. The proposed method was tested on a cantilever structure both experimentally and numerically. Six different damage scenarios including three different damage locations and three different damage severities were introduced to the structure. The results revealed that the proposed method was able to quantify different damage levels with a good precision.

A neuro-wavelet technique for seismic damage identification of cantilever structures

A method based on artificial neural networks and wavelet transform is proposed for identifying seismic-induced damage of cantilever structures. In the proposed method, response accelerations are measured at strategically selected locations. To extract damage-induced sharp transitions from the measured signals, they are decomposed by continuous wavelet transform. The size of the decomposed signals is reduced by principal component analysis (PCA). Principal components obtained from PCA are fed to a set of neural networks to identify damage. The proposed algorithm is applied to a tall airport traffic control tower by means of numerical simulations. The obtained results show that the proposed method effectively identifies seismic-induced damage, and the noise intensity has a negligible effect on the predicted results. Moreover, the trained neural network system is able to predict the seismic-induced damage of unseen samples well.

Seismic performance evaluation of an airport traffic control tower through linear and nonlinear analysis

Due to a lack of adequate information about seismic design and the performance of airport traffic control (ATC) towers, structural engineers often rely on building codes. However, seismic performance and the demands of ATC towers differ significantly from common structures. In this paper, the seismic performance of Kuala Lumpur International Airport traffic control tower, with a height of 120 m, was investigated. The results showed that in comparison to modal response spectrum analysis, equivalent static analysis overestimated overturning moments, drifts, maximum displacement and demand/capacity ratio. In addition, linear analysis underestimates base shear, drifts and overturning moments in comparison to the results of nonlinear time history and pushover analysis.

Prionljivost armaturne šipke u spoju od polimera armiranog vlaknima

U ovom se radu prikazuje ispitivanje prianjajna i proklizavanja armaturne šipke u novorazvijenoj injektiranoj spojnici sa staklenim vlaknima (eng. glass fiberreinforced polymer GFRP). Ukupno dvadeset sedam uzoraka ispitano je postupnim povećavanjem osnog vlačnog opterećenja. Rezultati dobiveni ispitivanjem uzoraka usvojeni su za modeliranje ovisnosti naprezanje prianjanja proklizavanje, što je uspoređeno sa zahtjevima iz normi i odredbi. Rezultati pokazuju da se u konusnim spojnicama razvija veća čvrstoća prianjanja i otpornost na opterećenje usporedo sa smanjenjem promjera u srednjem dijelu.

Development of delta wing aerodynamics research in Universiti Teknologi Malaysia low speed wind tunnel

This paper presents wind tunnel experiment on two delta wing configurations which are differentiated by their leading edge profiles: sharp and round-edged wings. The experiments were performed as a part of the delta wing aerodynamics research development in Universiti Teknologi Malaysia, low speed tunnel (UTM-LST). Steady load balance and flow visualization tests were conducted at Reynolds numbers of 0.5, 1, and 1.5 × 106, respectively. The flow measurement at low Reynolds number was also performed at as low as speed of 5 m/s. During the experiments, laser with smoke flow visualizations test was performed on both wings. The study has identified interesting features of the interrelationship between the conventional leading edge primary vortex and the occurrence and development of the vortex breakdown above the delta wings. The results conclude the vortex characteristics are largely dependent on the Reynolds number, angle of attack, and leading-edge radii of the wing.

Grouted Pipe with Double Spirals for Precast Concrete Connections

This paper presents the pullout performance of grouted splice connections made with steel pipes and double spirals in connecting high tensile steel deformed bars. The parameters studied were the steel bar embedded lengths, grout strength and diameter of the pipe in influencing the tensile performance of the splice connections. A total of nine proposed grouted spiral connections with double spirals were tested under increasing axial tension until failure. The results indicated that the use of double spiral combined with grout strength of at least 60 N/mm2 and main steel bar embedded length of 10 times bar diameter could provide adequate bond strength to form a satisfactory precast connection system.

Performance of Grouted Splice Sleeves with Tapered Bars under Axial Tension

Many structural failures in precast concrete buildings are initiated by connection failures. To avoid such failures, the connections should have enough strength to join the reinforcement bars between precast concrete panels. This paper presents the structural performance and behaviour of a proposed splice sleeve connection using generic steel pipe. The connection consisted of steel bars with tapered nuts confined in grouted steel pipes. The connections were subjected to increasing axial tension until failure. The results show that the use of smaller pipes gives better confinement effects and provide higher bond strength. A short embedment length of about 10 times rebar diameter is able to provide full tensile strength of the connected rebars. As compared to long embedment length of conventional lapping of steel bars, the proposed connection is able to provide structural continuity with short embedment length.