<p>The Bach Dang Bridge forms part of the Ha Long – Hai Phong Highway in Vietnam. It will help cut 50km from the journey between Hanoi and the Ha Long Bay UNESCO world heritage site. The focal cable-stayed section of the bridge will consist of two main spans of 240 m. The tallest of the three towers will reach a height of almost 100 m.</p><p>The construction technique used for the cable-stayed section is to cast 9.6 m-long and 28 m-wide concrete segments in situ, using an underslung form traveller (FT) which is launched to the next position once the segment is cast.</p><p>The FT has been designed by the Technical Centre of specialist contractor VSL. Its weight is minimised by using the stay cable as a support at the front of the traveller. The stay cable is connected to the FT by precasting the anchor block and securing it to the FT. This innovation was previously, successfully used by VSL on the Ironton-Russell project in the USA. Besides, the formwork system has been mechanised to be easily collapsed from one segment to the next.</p><p>This paper discusses the design of this innovative construction technique and how it was used on this major bridge project in Vietnam.</p>
During the periodic inspection of the Alvheim subsea system 2013 a number of cracks were observed at the Mid Water Arch (MWA) tether anchoring arrangement. The MWA and associated anchor block are critical design elements. Detailed investigations were initiated in order to determine future development of the cracks and their severity.
The application of advanced non-linear finite element analysis as part of the inspection and maintenance strategy resulted in significant cost savings compared to a solution based on immediate mitigation action.
This paper describes the background for occurrence of these cracks and the analyses used to determine their development:
• The cracks are located in non-loadbearing locking brackets. The function of the brackets is primarily to secure the pins connecting the top part of the tether hinge to the anchor block.
• During construction the locking brackets were welded to the pin and to the tether hinge. This way the non-structural element became part of the load bearing system resulting in very high stresses in the bracket and subsequent crack development. It could not immediately be excluded that the cracks observed could initiate further cracking into main bearing parts of the hinge.
• FE modeling using Abaqus [1] was used to analyze the criticality of the situation. Non-linear material properties and removal of elements were applied in order to simulate crack initiation and crack growth.
The system was analyzed by modelling the load paths from initial assembly on land, installation loads and finally the loads during operation. Removal of elements was introduced to replicate the crack growth pattern observed on ROV still photos from periodic surveys 2012 and 2013.
The analysis documented the principle mechanism behind the crack development and further demonstrated that the risk of failure of any of the load bearing elements was negligible.
The results of the analysis provided the necessary documentation for the appropriate precautions and at the same time plan for execution of mitigation measures which would have minimal economic impact.
Based on pit excavation of Shenzhen Airport Rail transport hub project, combined with anchorage stress characteristics, difficulties was studied and numerical calculation for the envelope structure was undertaken. The successful application of design provides new ideas, improved design methods for super soft soil foundation engineering, which can greatly promote the application and development of anchor block in soft foundation excavation.
AbstractThree different dispersants, a low molecular weight compound (aminoalkanol), a polymer (polyelectrolyte) and a block-co-polymer (block polyethylenoxide-polyacrylic acid) were investigated with AFM and rheology in an aqueous system in order to elucidate the influence of the size and structure of the molecule on the dispersion stabilization. The AFM studies indicate that the aminoalkanol gives repulsive forces due to electrostatic repulsion only. The polyelectrolyte seems to stabilize the dispersion with both steric and electrostatic repulsive forces. A new compound that was designed for pure steric stabilization in aqueous media a block-co-polymer consisting of a polar anchor block and a stabilizing neutral chain was investigated for its behavior. The AFM measurements show that it is likely that this compound causes repulsion of silicon nitride surfaces due to steric repulsion only. Rheological measurements of aqueous powder slurries show that the adsorption of the organic additives is of great importance. Due to a more silicon dioxide like acidic surface of the investigated Si3N4 - powder the carboxylate anions of the block-co-polymer adsorb badly. Therefore, no sterically repulsive forces can be built up. This then causes an increase in the slurry's viscosity.
FUNDAMENTAL STUDY ON THE STRENGTH OF JOINTS IN REINFORCED CONCRETE PRECAST STRUCTURES : Properties of the bearing capacity of a inserted bar with an anchor block and the stress distribution of concrete and its bearing capacity under the concentrically loaded out of the Inside Part I