Moment-less Arches for Reduced Stress State

This paper presents a study of two-pin arches of constant cross-section that are moment-less under statistically prevalent (permanent) load. The arches are defined by analytical form-finding previously reported in [1]. The work provides guidance regarding the solution process, and expressions for reactions and axial forces. New analytical results include the derivation of the arch length, and a method for finding co-ordinates of individual arch segments in pre-fabricated construction. The accuracy of the shape prediction for inextensible moment-less arches is good, compared to the results from elastic models. Case studies report on medium and large-span arches, with the latter resembling the iconic Hoover Dam arch. Comparative studies of the moment-less and conventional arch forms (mostly of parabolic configuration), are carried out using permanent and variable loads. Additionally, the Hoover Dam arch is analysed for a discrete load transfer from the deck. Circular arches are analysed for the permanent load only, and are shown to be extremely inefficient in load resistance. Moment-less arches are found to provide a minimal stress response to loading and require least amount of material – a feature observed in natural objects. These characteristics are important from a durability perspective – a key concern for our future infrastructure.

Finding the optimum layout for cable-stayed bridge in conceptual design

<p>In the cable-stayed bridges the primary cost components of the load-bearing material, in the longitudinal direction of the bridge, are the cables. The longer the bridge, the higher the share of the costs of the load-bearing material. The quantity of the cables and the cost optimized cable and tower topology can be reliably solved, already in very early design stages, using a simple calculation method proposed in this article. The cables are considered as a curtain structure and the cable forces are calculated for the permanent load balance. The solutions are performed mathematically by using integral calculus based on a force length method and a unit bridge concept. The results provide a good idea of the optimum pylon height for both one-pylon and two-pylon bridges. The optimum pylon height depends on the span ratio and the chosen cable system.</p>

Permanent glass-fibre-reinforced under water concrete floor

<p>Glass fibre reinforced polymer (GFRP) has been applied in underwater concrete floors as part of the permanent structure of two underpasses within a road upgrade project in The Netherlands. This application is unique in view of the permanent nature of the use of GFRP in such structures. These underwater concrete floors are subjected to both downwards loads, such as traffic loads and permanent load, as well as by water pressure uplift.</p><p>The construction pit consists of permanent sheet piling with a prefab concrete deck on top and a permanent underwater concrete floor between the sheet piling. This permanent underwater concrete floor is reinforced with only GFRP reinforcement. The fibre prevents cracking in the outer zone and increase the tensile strength.</p>

Conceptual Design of balanced Cable-Stayed Bridges

<p>The cables are the major loadbearing cost components in the longitudinal direction of a cable-stayed bridge. The quantity of the cables reflects directly to the comparative costs of different alternative layouts. The cable forces, calculated for permanent load balance lead to a reliable cable quantity estimation. For a long-term durability it is important that the bridge is in balance for permanent loads. The influence of the live loads can be estimated separately.</p><p>The purpose of this article is to estimate cable quantities in an early design stage when finding the optimum solution for the bridge. A simple solution method is carried out mathematically using vector algebra and the force length method. This article sets a clear path for determining the preliminary cable forces and cable quantities for two-pylon and single-pylon cable-stayed bridges. The variables are the span length relation, pylon height relation to the main span length, optimum cable anchorage distance at the pylon and the permanent load of the deck.</p><p>Also, the cable quantities of single-pylon bridges can be calculated, even for bridges with highly asymmetric spans. It is noted that the single-pylon cable-stayed bridge has remarkably bigger cable quantity than the two- pylon bridge with equal length.</p><p>The results reveal that the optimum cable anchorage distance in the pylon depends on the pylon height. The higher the pylon is, the greater the optimum anchorage distance should be.</p><p>For the durable bridge an optimum layout and a good balance for gravity loads with minimized bending moments are an important design target. The article helps in reaching that target.</p>

Reflections on New Zealand’s earthquake resistant design approach

Perceived shortcomings in NZS 1170.5 [1] and some other Standards are highlighted and areas for improvement are suggested. A particular focus is placed on achieving the principal objective of achieving life safety at the limit state at which structural collapse is to be avoided. Topic areas commented on include: The objectives of earthquake resistant design, especially that of avoiding the collapse of structures The appropriateness of current classifications of buildings into importance levels The currency and adequacy of the design seismic hazard spectra requirements The justification for, and application of, a structural performance factor The force-based and displacement-based methods of analysis and design, and the effects of plastic hinging relieving member permanent load moments at plastic hinges adjacent to points of support Consideration of displacement effects, and effects on displacements, at the limit state at which collapse is to be avoided Achieving reparability Some shortcomings in the material Standards for both structural steel and reinforcing steel Consideration of site conditions, and in coastal locations the tsunami risk Comparability of New Zealand design requirements with other major design codes.

Cable Replacement of the Tacitus Cable Stayed Bridge

As part of a major renovation programme of critical highway infrastructure in the Netherlands, the Tacitus Bridge at Ewijk, a 1055-metre-long orthotropic steel box girder deck of ten spans, with a main cable-stayed span of 270 metres, has undergone extensive strengthening and refurbishment. Due to the presence of micro-fissure defects identified in the existing lock coiled stay cables and an increase in permanent load on the bridge deck resulting from the addition of a high strength concrete overlay acting compositely with the orthotropic steel deck, it was concluded that the existing stay cables needed replacement. This paper presents the analytical approach developed to verify that the existing stay cables could be removed with no additional temporary supports and the use of advanced non-linear techniques to predict and monitor the performance of the bridge during each step of destressing the existing stay cables and of tensioning the new parallel strand cables.

Research and Design of Fixed Photovoltaic Support Structure Based on SAP2000

In the solar photovoltaic power station project, PV support is one of the main structures, and fixed photovoltaic PV support is one of the most commonly used stents. For the the actual demand in a Japanese photovoltaic power, SAP2000 finite element analysis software is used in this paper, based on Japanese Industrial Standard (JIS C 8955-2011), describing the system of fixed photovoltaic support structure design and calculation method and process. The results show that: (1) according to the general requirements of 4 rows and 5 columns fixed photovoltaic support, the typical permanent load of the PV support is 4679.4 N, the wind load being 1.05 kN/m2, the snow load being 0.89 kN/m2 and the seismic load is 5877.51 N; (2) by theoretical calculation of the two ends extended beam model, the beam span under the rail is determined 2200 mm; (3) by the way of using the single factor experiment, through the calculation and analysis of SAP2000, the three best supporting points of the support of the W stent are determined; (4) by comprehensive simulation, the optimal parameters for the rail, beam, support and bolt are 60× 60× 1.0, 60× 60× 1.0, 40× 50× 2.0, and M10 respectively.

Effect of Polypropylene Fibres on the Thermal Conductivity of Lightweight Foamed Concrete

With the reduction in the permanent load on the structure and excellent insulation properties, the lightweight foamed concrete is a potential thermal insulating building material to counter the urban heat island effect, which increases the temperature of urban areas due to the concentration of infrastructures constructed using conventional concrete that absorbs the solar radiation. The lightweight foamed concrete whose dry density ranges from 400 kg/m3 to 1600 kg/m3, has lower thermal conductivity compared to conventional concrete. But reduced density attributes to reduced compressive strength. In this study, to enhance the mechanical properties, the foamed concrete of 1600 kg/m3 density is reinforced with polypropylene fibres (PP). Four percentages of PP fibres, 0% (controlled), 0.2%, 0.25% and 0.30% were added into the foamed concrete. The compressive strength as well as the thermal conductivity of foamed concrete reinforced with PP fibres were determined. Based upon the findings, the optimum percentage of PP was determined to be 0.20% which gave higher compressive strength while thermal conductivity of foamed concrete was observed to decrease upon addition of PP fibres. Thus, addition of PP fibres improves the thermal resistance in the foamed concrete along with enhancing the mechanical properties.

Electrochemical investigation of corrosion and repassivation of structural aluminum alloys under permanent load in bending

This work reports an electrochemical investigation of corrosion and repassivation in NaCl solutions of structural Al 7075-T6 and Al 2024-T3 as a function of permanent load in bending by means of single-cycle anodic polarization. Experimental variables other than the load level were the extent of corrosion, chloride ion concentration and initial pH of the test solution, in addition to the pre-exposure in the aggressive environment and of the viscosity of the test solution for Al 7075-T6. The susceptibility to local stress during corrosion and repassivation depends on the alloy microstructure and corrosion mechanisms. In the case of Al 2024-T3, the mechanical activation is driven by cathodically controlled dissolution of this alloy at open circuit in concentrated NaCl, being indicative of a chemomechanical effect. Conversely, for Al 7075-T6, the effect of applied load is better discerned from the repassivation response. Film rupture/formation sequence and related interfacial (electro)chemical processes determine the stress-enhanced metastable repassivation of this alloy.