Bambang Suhendro

Modified Chicken Claw (Cakar Ayam Modifikasi) System - A New Concept in Green Pavement Technology over Soft and Swampy Ground

Some parts of Indonesia region, especially near the coast, have soft subgrade and a part of them is swampy with relatively deep soft soil layer. To utilize and develop such areas absolutely need an adequate road network, while the existing road on such areas needs high maintenance cost. Conventional solutions with embankment made of better soil properties through preloading process, or with the technology of slab on pile system, is expensive and not environmentally friendly. This paper discusses the basic principles, methods of analysis and design, implementations, and practical applications of the Modified Chicken Claw (Cakar Ayam Modifikasi) system, which in addition to technically meets the requirements, is also relatively much cheaper, easier and faster to construct, and more environmentally friendly. This is a totally new concept of pavement system originally developed in Indonesia, which has been widely applied as road construction over soft and swampy grounds with satisfactory long-term performance. The system consists of a relatively thin (10~15 cm) reinforced concrete slab, pipes (chicken claws) inserted into the soft ground at about 2.5 m distances as slab stiffener, and underlying soft soil layer. Compared to previous similar versions, the Modified Chicken Claw system has many advantages including (a) a much more accurate method of analysis and design so as to obtain optimal design, (b) much smaller dimension and chicken claw weight, (c) vertical concrete fin as underlying soil barrier for more pavement stability and durability, (d) the present of thin asphalt layer to significantly reduce the effect of cyclic thermal loading and act as wearing course, (e) combination with a light fill material to minimize the consolidation settlement, and (f) a much shorter construction time with a relatively cheaper cost, since heavy equipment are not necessary.

Numerical Investigation on the Buckling Failure of Slender Tubular Member with Cutout Presence

Pitting corrosion often leads to the creation of small holes in steel tubular member of platform structures when a protective coating is damaged. A single pit on slender compression element can cause a significant reduction in the buckling capacity of the member. Euler formula is no longer applicable for determining the critical buckling load when cutout presence on the member. This research was conducted to numerically study the effect of a circular hole on the buckling capacity of slender steel tubular member. A variation on hole positions was at 0.125 L, 0.25 L, 0.375 L, and 0.5 L, where L is the length of the member. The hole was taken to be 0.5 pipe diameter. Two nonlinear geometric 3D Finite Element models were developed to analyzed the member critical buckling load: (a) buckling analysis, where the problem was formulated as eigenvalue problem based on the nonlinear incremental equilibrium equations, and (b) nonlinear analysis, where the nonlinear equilibrium equations were developed and solved by several schemes to get the load – deflection curve. For the both models, the tubular member was discretized into: (a) shell elements, and (b) solid elements. The numerical results were verified by experimental investigation. The results showed that: (a) the presence of cutout reduced the buckling load significantly, (b) the reduction ranging from 3% to 10% depending on the hole positions, (c) the maximum reduction occurs when the hole position was in the middle of the member length, (d) compared to experimental results, the critical buckling load obtained from buckling analysis deviated 1~4% while those of nonlinear analysis deviated 1~5%, (e) the buckling mode corresponded with member bent away to opposite side of the cutout position.

The Damping Mechanism of Steel-Rubber Composite Beam under Flexural Dynamic Excitation

Damping is one of the several important parameters in the dynamic system. It reduces amplitude response of a structure, especially around the resonance. The higher the damping, the better the performance (more comfort, lower stress, less fatigue), and the longer the life cycle of the structure will be. There are many types of damper amongst other is the tuned mass damper (TMD), where mass and spring are designed in such that the TMD frequency is close to the natural frequency of the structure in question where the phase angle is about 180 degree out of phase. Applying steel-rubber composite beam as a damper in the TMD system is expected to increase the damping of the structure of interest. The objective of this study is to test experimentally and numerically the dynamic parameters of the rubber-steel composite beam upon a cantilever support system under static load-displacement test and flexural dynamic excitation. The addition of steel (in the form of wire mesh) embedded in the rubber beam significantly increases the stiffness, but the damping ratio, at a small range of displacement. The effectiveness of rubber material in the steel-rubber composite beam is expected when large displacement occurs, meaning that more energy dissipation and larger damping ratio. The established numerical model is able to generate dynamic parameters close to results of the experimental model, but the damping ratios.

Numerical, analytical and experimental prediction of force of solid cylindrical steel beam subjected to axial tension force using vibration technique

Vibration method is widely used to estimate axial force of string and beam element by using natural frequency. This paper demonstrates the use of vibration method to estimate the force of beam element. The specimen has ratio of length to diameter of 79.68. The specimen was subjected to the axial tension which was applied increasingly from 1000 N up to 20000 N. Numerical and analytical calculation modeling were used to predict the natural frequency of the solid cylindrical steel beam. Experimental research was also used to verify the value of natural frequency of the specimen. The results showed that the natural frequency of analytical and numerical calculation is in line with experimental results in the first mode of natural frequency.

Differential Settlement of Rigid Pavement of 3-Pile Row Nailed-slab System on Soft Clay Sub Grade Due to Monotonic and Repetitive Loadings

A new kind of rigid pavement is Nailed-slab System. It is not a soil improvement method, but rather as an alternative method to improve the performance of rigid pavement on soft soils. This system consists of a thin reinforced concrete slab, and short piles attached underneath. The installed piles under the slab were functioned as slab stiffeners and anchors. This research is aimed to learn the deflection behavior of Nailed-slab System by conducting full scale testing model. The tested full scale model was 6.00 m x 3.54 m slab area with 0.15 m in slab thickness, and consists of 15 short micro piles (0.20 m in diameter, 1.50 m in length, and 1.20 m in pile spacing) as slab stiffener, piles and slab was connected monolithically by using the slab thickening (0.40 m x 0.40 m in area and 0.20 m in thickness), then in due with vertical concrete wall barrier on the two ends of slab. Nevertheless, the testing results show good performance. The model experienced very small deflection and has higher bearing capacity above 160 kN because of the linear elastic-response is kept until load 160 kN. Loading position was not significantly influenced to the maximum deflection and bearing capacity. Differential settlement due to monotonic loadings tend higher than the one caused by repetitive loadings for interior loading. All total and differential settlements were smaller than allowable deflections.

Small-scale experimental investigation on the behaviour of nailed slab system in expansive soil

Nailed slab system has been developed as an alternative rigid pavement on unstable soils such as soft soil and expansive soil. Nailed slab system is a rigid pavement system, which consists of a thin plate (thickness 12 cm-20 cm) reinforced with micro piles with a diameter of 15 cm-20 cm and a length ranging from 1.5 m − 2.0 m. On soft soil, the nailed slab system can increase the modulus of subgrade reaction and shows better performance than conventional rigid pavement systems in their ability to support the load. However, behaviour nailed slab system on expansive soil still needs to be researched. This research aims to study the behaviour of nailed slab system on expansive swelling soil under heavy and loading test. On expansive soil, nailed slab system was subjected to uplift force due to the soil expansion. Small scale experimental models have been done in the laboratory. Nailed slab system models with a variation in the length of piles have been made. The test results showed upward displacement on nai...