A novel analysis technique is introduced for efficient modelling of box girder bridge decks. The general three-dimensional equations used to accurately define the deformation of these complex beam-like slender structures are decoupled into a two-dimensional cross-sectional problem and a one-dimensional beam problem through decomposition of the three-dimensional strain field. The two-dimensional cross-sectional problem is solved by a two-dimensional finite element analysis considering in-plane as well as out-of-plane warping displacements of the beam section. This gives an accurate constitutive relationship of the one-dimensional beam problem without making any major assumptions as is often done in usual beam theories. The one-dimensional beam problem is solved by a one-dimensional beam finite analysis and the results obtained are used to recover three-dimensional stress, strain and displacement fields accurately. Numerical examples of box girder bridge deck systems having thin-walled sections are solved by the proposed approach to show its performance.
Abstract:Terrorist attacks using improvised explosive devices (IED) can result in unreinforced masonry (URM) wall collapse. Protecting URM wall from IED attack is very complicated. An effective solution to mitigate blast effects on URM wall is to retrofit URM walls with metallic foam sheets to absorb blast energy. However, mitigation of blast effects on metallic foam protected URM walls is currently in their infancy in the world. In this paper, numerical models are used to simulate the performance of aluminum foam protected URM walls subjected to blast loads. A distinctive model, in which mortar and brick units of masonry are discritized individually, is used to model the performance of masonry and the contact between the masonry and steel face-sheet of aluminum foam is modelled using the interface element model. The aluminum foam is modelled by a nonlinear elastoplastic material model. The material models for masonry, aluminum foam and interface are then coded into a finite element program LS-DYNA3D to perform the numerical calculations of response and damage of aluminum foam protected URM walls under airblast loads. Discussion is made on the effectiveness of the aluminum foam protected system for URM wall against blast loads.Unreinforced masonry (URM) construction is extremely vulnerable to terrorist bomb attacks due to the effects of the powerful pressure wave at the blast front that strikes buildings unevenly and may even travel through passageways, resulting in flying debris that is responsible for most fatalities and injuries. An effective solution to mitigate blast effects on URM construction is to strengthen the masonry using retrofit technologies. However, retrofit URM constructions is currently in their infancy in the world [1,2] . Categories of available masonry retrofit include: conventional installation of exterior steel cladding or exterior concrete wall, and new technologies such as external bonded (EB) FRP plating, metallic foam cladding, sprayed-on polymer and/or a combination of these technologies [3,4] . But limited research has been conducted to investigate retrofit technique to strengthen URM walls against blast loads [5,6] . Therefore, it is urgent to study the behaviours of retrofitted URM walls under blast loads, and develop an efficient mitigating solution to enhance blast resistance of URM construction.Metallic foams have excellent properties that can mitigate the effects of an explosive charge on a structural system. Recently, blast tests on aluminum foam protected RC structural members have been conducted and it was found that aluminum foam is very effective to absorb blast energy and thus effectively protect RC structural members against blast loads [7] . It is believed that aluminum foam is also very effective for protection of URM construction against blast loads. Since field blast tests are very expensive and sometimes not even possible to conduct due to safety and environmental constraints, numerical simulations with validated model provide an alternative method for an extensive ...
Many operators in Kazakhstan are producing from carbonate reservoirs with fairly low permeability and porosity with the presence of dominant natural fractures. The completion and perforation of the reservoir are critical phases during which special attention must be placed on the well cleanup to obtain the maximum hydrocarbon productivity. Wells in the tight carbonate formation of certain fields in western Kazakhstan have historically been perforated in overbalance conditions or in static underbalance conditions that require killing the well immediately after the perforation for installing the permanent completion. After the permanent completion has been put in place, an acid wash must be performed to remove all the damage induced by the killing operation and the perforating debris. Both ways of perforating the wells expose the reservoir to potentially damaging fluids during and after the perforation. The exposure time of these fluids can be prolonged if adverse meteorological conditions are encountered. The damaging fluids can significantly impair the productivity by blocking the newly perforated tunnel, as well as by filtering through the natural fractures, which in turn makes it very difficult to remove even after as acid wash. As a result, the wells do not produce to their full potential. A new perforating approach utilizing a dynamic underbalanced technique, in conjunction with a solids-free, viscoelastic-based, fluid loss pill, was introduced in several new wells in western Kazakhstan for a major operator. The fluid loss pill was designed to be solids-free and to be easily broken, leaving no residue downhole. There were four main requirements for the fluid pill: Effective—capable of stopping or minimizing completion brine losses at bottomhole static temperatures (BHSTs) up to 137°C. Degradable—easy to clean and with minimal residual damage to the reservoir or the perforations. Compatible—fully compatible with reservoir fluids and any well service fluids. Solids-free—making the post-completion cleanup operation easy. The carbonate reservoir where this new approach was utilized has permeabilities varying from 6 to 38 mD, while the present reservoir pressure is approximately 4,200 psi at the reference depth of 3550 m. The new perforation approach allowed obtaining a cleaner perforation tunnel, increasing the average production compared with wells draining from the same reservoir that were completed with the traditional technique. The average production obtained with the new approach is approximately double that of the conventional technique. This has been verified on a campaign carried out on 11 wells, all located in the same area of the field, four of which were completed with the new perforation approach. Several other treatments have been performed and have indicated similar trends in production.
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