The effective length of columns in multi-storey frames

Codes of practice rely on the effective length method to assess the stability of multi-storey frames. The effective length method involves isolating a critical column within a frame and evaluating the rotational and translational stiffness of its end restraints, so that the critical buckling load may be obtained.The non-contradictory complementary information (NCCI) document SN008a [1] to BS EN 1993-1 [2] provides erroneous results in certain situations because it omits the contribution made to the rotational stiffness of the end restraints by columns above and below, and to the translational stiffness of end restraints by other columns in the same storey.Two improvements to the method are proposed in this paper. First, the axial load in adjoining columns is incorporated into the calculation of the effective length. Second, a modification to the effective length ratio is proposed that allows the buckling load of adjacent columns to be considered. The improvements are shown to be effective and consistently provide results within 2% of that computed by structural analysis software, as opposed to the up to 80% discrepancies seen using the NCCI [1]

Shear strengthening of continuous reinforced concrete T-beams using deep embedment technique

Despite numerous studies, shear behaviour before or after strengthening is still not fully understood, particularly in continuous concrete structures which are the norm. Upgrading shear resistance is altogether more difficult since Externally Bonded Reinforcement (EBR) or Near Surface Mounted (NSM) techniques do not allow the FRP material to be anchored into the compression zone of the T-beams and they cannot be used in cases where the sides of the beams are inaccessible. An innovative retrofit technique, named Deep Embedment (DE) or Embedded Through Section (ETS) technique involves the insertion of FRP/steel bars upwards into vertical or inclined holes which have been drilled from the soffit of concrete beams. In this way, the tension and compression chords of the beams are directly connected while the bars are bonded to the concrete core through adhesives. With this technique strengthening can be done in cases where the webs are inaccessible. Thus the main focus of this study is to significantly contribute to the current knowledge on the behaviour of Reinforced Concrete continuous T-beamsstrengthened in shear using the DE technique where large shear forces are combined with large negative bending moments. An experimental program consisting of ten two-span continuous T-beams designed to fail in shear wascarried out in order to significantly contribute to the current knowledge on the behaviour of RC continuous Tbeams strengthened in shear using this technique. Therefore, this paper reports on the test results and on their significance in being able to apply this technique on concrete structures by validating them through adequate analytical models

Anchorage and residual bond characteristics of 7-wire strand

© 2017 Elsevier Ltd The periodic assessment of our existing concrete infrastructure is a crucial part of maintaining appropriate levels of public safety over long periods of time. It is important that realistic predictions of the capacity of existing structures can be made in order to avoid unnecessary and expensive intervention work. Assessment is currently undertaken using codified models that are generally readily applied to infrastructure with simple geometric and reinforcement details that conform to design methods for new structures. This approach presents two significant challenges for prestressed structures: (1) design and construction practice has changed significantly in the past 50 years, and modern codified approaches can be incompatible with historic structures; and (2) deterioration of exposed soffits can lead to reduced cover to internal prestressing strand. Unless appropriate reductions are used in assessment of a structure with such problems, unnecessary load restrictions, or major strengthening or reconstruction work may be required, despite having carried a full service load since its construction. There are currently no widely accepted methods for the prediction of peak and residual capacities in prestressed concrete beams with inadequately detailed 7-wire strand. This paper presents a completely new prediction methodology, validated against new experimental results from 31 novel semi-beam tests. The proposed models for peak load, residual load, and bond stress-slip modelling provide reliable, accurate, and conservative results. Their results demonstrate feasible and appropriate capacity reduction factors for use in the assessment of existing concrete infrastructure

Concrete structures using fabric formwork

Using fabric formwork, it is possible to cast architecturally interesting, optimised structures that use up to 40% less concrete than an equivalent strength prismatic section, thereby offering the potential for significant embodied energy savings in new concrete structures. This paper reports on the philosophy of and background to fabric formwork before techniques for the design, optimisation and shape prediction of fabric formed concrete beams are presented. The practicality of construction with non-orthogonal elements is discussed before the results of new structural test data, undertaken at the University of Bath on 4m span ’T’ beam elements formed in reusable fabric moulds, are presented. Potential areas of future development for fabric formwork, including the use of woven advanced composite fabrics as permanent participating formwork and the feasibility of uniform strength prestressed beams, are then discussed The practicality of construction with non-orthogonal elements is discussed before the results of new structural test data, undertaken at the University of Bath on 4m span ‘T’ beam elements formed in reusable fabric moulds, are presented. Potential areas of future development for fabric formwork, including the use of woven advanced composite fabrics as permanent participating formwork and the feasibility of uniform strength prestressed beams, are then discussed

Shear design of circular concrete sections using the eurocode 2 truss model

The introduction of the Eurocodes for concrete design will alter the way that shear is approached for concrete structures. BS EN 1992-1-1 has adopted the variable angle truss model for shear, a more theoretically consistent approach than that used in BS 8110-1. The model is confidently applied to rectangular sections, but its applicability to irregular sections is less clear. In particular, the behaviour of circular concrete sections is not well defined. This paper is intended to satisfy a requirement for design guidance on this topic that has been recognised by key BSI Committees. Using both experimental and theoretical data, the Eurocode variable angle truss model for shear design is assessed and extended to circular columns

Minimising energy in construction: practitioners’ views on material efficiency

The built environment accounts for 39% of global energy related CO2 emissions, and construction generates 13% of global GDP. Recent success in reducing operational energy and the introduction of strict targets for near-zero energy buildings mean that embodied energy is becoming the dominant component of whole life energy consumption in buildings. One strategy that may be key to achieving emissions reductions is to use materials as efficiently as possible. Yet research has shown that real buildings use structural material inefficiently, with wastage in the order of 50% being common. Two plausible mechanisms are 1) that some engineers hold individual misconceptions, or 2) that inefficiency is a cultural phenomenon, whereby engineers automatically and unquestioningly repeat previous methods without assessing their true suitability. This paper presents a survey of 129 engineering practitioners that examined both culture and practice in design relating to material efficiency. The results reveal wide variations and uncertainty in both regulated and cultural behaviours. For the first time, we demonstrate that embodied energy efficiency is not a high priority, with habitual over-design resulting in more expensive buildings that consume more of our material resource than necessary. We show wide variability in measures that engineers should agree on and propose research through which these culture and individual issues might fruitfully be tackled within the timeframes required by climate science.EPSR

A new route to exposed thermal mass: Sound-absorbing poured concrete

This paper investigates the novel possibility of utilising the structural concrete floor slab as a means of providing additional mid- to low-frequency sound absorption through the addition of cavities on the ceiling side, formed using flexible formwork, acting as Helmholtz resonators. Mid- to low-frequency sound absorption in rooms is typically achieved through the use of perforated plasterboard or a suspended tile-in-grid system. Such an approach can separate the room from the thermal mass of the ceiling above, leading to higher peak temperatures or increased cooling load. Suspended ceilings can also increase the embodied energy of the building and limit the potential for stack effect ventilation by reducing room height. In this work, frequency-dependent absorption coefficients of perforated concrete samples were measured using an impedance tube test. The results were found to agree with a theoretical analysis, suggesting that it would be relatively easy to predict the performance of perforations of other depths and diameters including those targeted at absorbing higher frequencies. Practical application: The measurements indicate that such a slab could be used as a practical replacement for perforated plasterboard or a tile-in-grid system. This would allow the slab to be tuned to the building’s acoustic performance and structural requirements. The approach has the potential to: (1) reduce the embodied and operational energy of buildings; (2) improve thermal comfort and (3) create a better acoustic environment in situations where surface robustness or longevity is important, for example public stairwells, pathways under roads and metro stations. </jats:p

The Genetics of Adaptation for Eight Microvirid Bacteriophages

Theories of adaptive molecular evolution have recently experienced significant expansion, and their predictions and assumptions have begun to be subjected to rigorous empirical testing. However, these theories focus largely on predicting the first event in adaptive evolution, the fixation of a single beneficial mutation. To address long-term adaptation it is necessary to include new assumptions, but empirical data are needed for guidance. To empirically characterize the general properties of adaptive walks, eight recently isolated relatives of the single-stranded DNA (ssDNA) bacteriophage φX174 (family Microviridae) were adapted to identical selective conditions. Three of the eight genotypes were adapted in replicate, for a total of 11 adaptive walks. We measured fitness improvement and identified the genetic changes underlying the observed adaptation. Nearly all phages were evolvable; nine of the 11 lineages showed a significant increase in fitness. However, fitness plateaued quickly, and adaptation was achieved through only three substitutions on average. Parallel evolution was rampant, both across replicates of the same genotype as well as across different genotypes, yet adaptation of replicates never proceeded through the exact same set of mutations. Despite this, final fitnesses did not vary significantly among replicates. Final fitnesses did vary significantly across genotypes but not across phylogenetic groupings of genotypes. A positive correlation was found between the number of substitutions in an adaptive walk and the magnitude of fitness improvement, but no correlation was found between starting and ending fitness. These results provide an empirical framework for future adaptation theory

Spatiotemporal control of mitotic exit during anaphase by an aurora B-Cdk1 crosstalk

According to the prevailing ‘clock’ model, chromosome decondensation and nuclear envelope reformation when cells exit mitosis are byproducts of Cdk1 inactivation at the metaphase-anaphase transition, controlled by the spindle assembly checkpoint. However, mitotic exit was recently shown to be a function of chromosome separation during anaphase, assisted by a midzone Aurora B phosphorylation gradient-the ‘ruler’ model. Here we found that Cdk1 remains active during anaphase due to ongoing APC/CCdc20- and APC/CCdh1-mediated degradation of B-type Cyclins in Drosophila and human cells. Failure to degrade B-type Cyclins during anaphase prevented mitotic exit in a Cdk1-dependent manner. Cyclin B1-Cdk1 localized at the spindle midzone in an Aurora B-dependent manner, with incompletely separated chromosomes showing the highest Cdk1 activity. Slowing down anaphase chromosome motion delayed Cyclin B1 degradation and mitotic exit in an Aurora B-dependent manner. Thus, a crosstalk between molecular ‘rulers’ and ‘clocks’ licenses mitotic exit only after proper chromosome separation.We thank Eric Griffis, Jean-René Huynh, Claudio Sunkel, Jonathon Pines, Melina Schuh and Christian Lehner for the kind gift of reagents, and Marco Gonzalez-Gaitán for supporting OA during the final stages of this work. LPC is the recipient of a Marie Skłodowska-Curie Action fellowship (grant agreement 746515). EMS holds an FCT Investigator position and his work is supported by Fundac¸ ão para a Ciência e a Tecnologia (PTDC/BEX-BCM/0432/2014). This work was supported by R01GM107026 grant to TJM and a Commonwealth Honors College grant to CMC Confocal and FLIM microscopy data collection was performed in the Light Microscopy Facility and Nikon Center of Excellence at the Institute for Applied Life Sciences, University of Massachusetts Amherst with support from the Massachusetts Life Science Center. Work in the HM lab is supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 681443) and FLAD Life Science 2020