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A new automated analysis procedure designed to overcome limitations of the traditional thrust line analysis method for masonry gravity structures is presented. The procedure, termed thrust layout optimization (TLO), is capable of automatically identifying admissible thrust lines in masonry gravity structures comprising general arrangements of masonry blocks. The procedure employs a modified truss layout optimization with transmissible loads formulation, which means that an initial thrust line layout does not need to be specified in advance. Highly visual output is generated, allowing areas where tensile strength has been implicitly assumed to be clearly identified, which is beyond the scope of traditional thrust line analysis. Also, sliding failures can be modelled without difficulty. Finally, examples are used to demonstrate the efficacy of the TLO procedure; these show that thrust line bifurcations can be automatically identified in problems involving openings, and that there is no need to estimate the ineffective area in buttress wall problems, both issues for the traditional thrust line analysis method.

While many national health authorities, such as the American Heart Association, have long recommended low-fat (1%) or fat-free dairy products over those with full fat (≥3.25%), recent epidemiological research suggests beneficial health effects of full-fat dairy products. The objective of this pilot study was to determine the effect of substituting full-fat (3.25%) yogurt for fat-free yogurt on glucose and lipid metabolism in individuals with prediabetes. We hypothesized that short-term consumption of three daily servings of full-fat yogurt would improve glucose and lipid homeostasis. We conducted an 8-week randomized, double-masked, controlled crossover study in six men and seven women aged 45-75 years old to compare two diets, i) a lower-fat (30%) diet containing non-fat yogurt (NFY diet) and ii) a higher-fat diet (38%) consisting of full-fat yogurt (FFY diet), consumed for three weeks each. Dairy fat in the full-fat yogurt accounted for the arithmetic difference in fat (8% energy) between diets. At the end of each diet, blood was collected and an oral glucose tolerance test (OGTT) and mixed meal tolerance test (MMTT) were performed. The FFY diet resulted in a lower blood fructosamine concentration ( P=0.01). During the OGTT, fasting blood glucose and insulin concentrations were both lower in response to the FFY diet ( P=0.05 and P=0.03, respectively), but there was no change in the C-peptide concentration. In addition, no differences between the diets for the area under the curve for glucose or insulin concentrations were observed. At the 120-minute time point, there was no difference between the diets for glucose or insulin concentrations; however, C-peptide concentrations were lower in response to the FFY diet ( P=0.05). Though the Matsuda index did not differ between diets, the Homeostatic Model Assessment for Insulin Resistance value was lower in response to the FFY diet on the day of the OGTT ( P=0.03). During the MMTT, the area under the curve was lower for glucose ( P=0.02) and higher for insulin ( P=0.01) in response to the FFY diet. Blood triacylglycerol concentration and the total cholesterol to HDL cholesterol ratio were lower in response to the FFY diet ( P=0.01 and P This project was funded by National Dairy Council Nutrition Research Funding and a USDA Agriculture and Food Research Initiative National Institute of Food and Agriculture Predoctoral Fellowship. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A new interactive truss layout optimization web-app has been developed for educational use. This has been designed to be used on a range of devices, from mobile phones to desktop PCs. Truss designs are first generated via numerical layout optimization and then rationalized via geometry optimization. It is then shown that these designs can be simplified using a computationally inexpensive process that allows the user to control the trade-off between complexity and structural volume. The process involves the use of smooth Heaviside representations of member existence variables, with nodal slack forces employed that allow unstable intermediate truss structures. Full details of the web-app are provided in this contribution, from underlying formulation to cloud computing implementation. A range of numerical examples are used to demonstrate the efficacy of the web-app, and to show how it can potentially be used in educational and practical engineering settings.

Layout optimization provides a powerful means of identifying materially efficient structures. It has the potential to be particularly valuable when long-span structures are involved, since self-weight represents a significant proportion of the overall loading. However, previously proposed numerical layout optimization methods neglect or make non-conservative approximations in their modelling of self-weight and/or multiple load-cases. Combining these effects presents challenges that are not encountered when they are considered separately. In this paper, three formulations are presented to address this. One formulation makes use of equal stress catenary elements, whilst the other two make use of elements with bending resistance. Strengths and weaknesses of each formulation are discussed. Finally, an approach that combines formulations is proposed to more closely model real-world behaviour and to reduce computational expense. The efficacy of this approach is demonstrated through application to a number of 2D- and 3D-structural design problems.

Background In practice, prescribing of a GLP-1 agonist (GLP-1a) or SGLT-2 inhibitor (SGLT-2i) for patients with type 2 diabetes mellitus (T2DM) and multiple risk factors for atherosclerotic cardiovascular disease (ASCVD) may be lagging behind the guidelines that recommend it. We aim to increase the prescribing rates of GLP-1as and SGLT-2is in a primary care resident clinic. Methods Eligible patients included adults with T2DM in an internal medicine primary care resident practice at the University of Vermont who were not already taking a SGLT-2i or GLP-1a. These patients were offered a diabetes medication management (DMM) visit with their PCP. The residents participated in a 30-minute educational intervention on: prescribing guidelines, medication risks and side effects, counseling patients, dose titration, and current Medicaid and Medicare insurance coverage estimates. This information was summarized in two tables that were included in a templated progress note to be used for DMM visits. DMM visits took place over a six month period. Chart review was conducted to determine patient co-morbidities and outcomes of the initial and follow-up DMM visits. Additional data was gathered from a post-visit survey completed by resident PCPs. Data was analyzed using descriptive methods. Results One hundred sixteen patients with T2DM were eligible. Sixty-five patients either declined, could not be reached, or did not present for their scheduled appointment. Fifty-one patients (44% of those eligible) completed a DMM visit. Of these 51, 18 (35%) were started on a SGLT-2i, either at the initial visit or at a follow-up visit. A GLP-1a was started for 14 (27%) patients. Nearly all who completed a DMM visit had at least one risk factor for ASCVD, and most had multiple risk factors. Problem lists for these patients showed that 40 (78%) had hypertension, 33 (65%) had hyperlipidemia, 12 (24%) had coronary artery disease, and 5 (10%) were current smokers. Two (4%) had a diagnosis of CHF, and 12 (24%) had CKD. Forty (out of 46) (87%) survey respondents reported that they were "more likely" to prescribe SGLT-2is and GLP-1as after participating in the intervention. The two most common reasons that these medications were not prescribed were the presence of competing visit priorities and co-management of diabetes medications by an endocrinologist. Conclusions Most patients with T2DM also have risk factors for ASCVD and would benefit from a GLP-1a or SGLT-2i. Prescriber education is an effective way to expand prescribing of these medications. Primary care providers are well-positioned to consider patients’ cardiovascular co-morbidities when prescribing diabetes medications, but may also be burdened by other visit priorities taking precedence. This study highlights the importance of a team-based approach to diabetes management and demonstrates a role for enhanced communication between primary care and specialties such as endocrinology and cardiology. Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

Structural optimization methods can be extremely powerful when used at the initial, conceptual, design stage of a building or bridge structure, potentially identifying materially efficient forms that are beyond the imagination of a human designer. This is particularly important at present, given the pressing need to reduce the carbon footprint associated with the built environment in the face of the current climate emergency. In this contribution, a computationally efficient global-local optimization framework is proposed, in which a linear programming-based truss layout optimization step is employed to generate initial (near-)optimal designs, with a non-linear optimization step then used to generate designs that take account of real-world complexity. To facilitate rapid exploration of design concepts, the proposed global-local optimization framework has been made available in the Peregrine plug-in for the popular Rhino-Grasshopper parametric modelling environment. The efficacy of the approach is demonstrated through its application to a range of case study problems.

Traditional truss layout optimization employing the ground structure method will often generate layouts that are too complex to fabricate in practice. To address this, mixed integer linear programming can be used to enforce buildability constraints, leading to simplified truss forms. Limits on the number of joints in the structure and/or the minimum angle between connected members can be imposed, with the joints arising from crossover of pairs of members accounted for. However, in layout optimization, the number of constraints arising from ‘crossover joints’ increases rapidly with problem size, along with computational expense. To address this, crossover constraints are here dynamically generated and added at runtime only as required (so-called lazy constraints); speedups of more than 20 times are observed whilst ensuring that there is no loss of solution quality. Also, results from the layout optimization step are shown to provide a suitable starting point for a non-linear geometry optimization step, enabling results to be obtained that are in agreement with literature solutions. It is also shown that symmetric problems may not have symmetric optimal solutions, and that multiple distinct and equally optimal solutions may be found.

The well-known ‘ground structure’-based truss layout optimization method has recently been extended to allow accurate modelling of distributed self-weight. By incorporating equally stressed catenaries in the ground structure, non-conservative errors caused by neglecting bending effects within members carrying their own weight are eliminated. However, in cases where the self-weight of a structure has a favourable role in supporting the applied loads, solutions that include convoluted arrangements of overlapping elements may often be generated. To address this, an enhanced layout optimization formulation is proposed that explicitly allows inclusion of favourable unstressed masses, such as counterweights. Frictional supports are also modelled and the cost of abutments and anchorages taken account of in the formulation. The efficacy of the proposed methodology is demonstrated through application to benchmark examples and to the conceptual design of a simplified long-span bridge structure, considering both ground anchored and self-anchored alternatives.

Similar to other cropping systems, few walnut cultivars are used as scion in commercial production. Germplasm collections can be used to diversify cultivar options and hold potential for improving crop productivity, disease resistance and stress tolerance. In this study we explored the anatomical and biochemical bases of photosynthetic capacity in 11 J. regia accessions in the USDA-ARS National Clonal Germplasm Repository. Net assimilation rate (A) differed significantly among accessions and was greater in those from lower latitudes coincident with increases in stomatal and mesophyll conductance, leaf thickness, mesophyll porosity and gas-phase diffusion, and leaf nitrogen, and lower leaf mass and stomatal density. High CO-saturated assimilation rates led to increases in A under limiting conditions. Greater A was found in lower latitude accessions native to climates with more frost-free days, greater precipitation seasonality, and lower temperature seasonality. As expected, water stress consistently impaired photosynthesis with the highest % reductions in three lower latitude accessions (A3, A5, and A9), which had the highest A under well-watered conditions. However, A for A3 and A5 remained amongst the highest under dehydration. J. regia accessions, which have leaf structural traits and biochemistry that enhance photosynthesis, could be used as commercial scions or breeding parents to enhance productivity.

Copyright © The Author(s) 2021. Transmissible loads are external loads defined by their line of action, with actual points of load application chosen as part of the topology optimization process. Although for problems where the optimal structure is a funicular, transmissible loads can be viewed as surface loads, in other cases such loads are free to be applied to internal parts of the structure. There are two main transmissible load formulations described in the literature: a rigid bar (constrained displacement) formulation or, less commonly, a migrating load (equilibrium) formulation. Here, we employ a simple Mohr’s circle analysis to show that the rigid bar formulation will only produce correct structural forms in certain specific circumstances. Numerical examples are used to demonstrate (and explain) the incorrect topologies produced when the rigid bar formulation is applied in other situations. A new analytical solution is also presented for a uniformly loaded cantilever structure. Finally, we invoke duality principles to elucidate the source of the discrepancy between the two formulations, considering both discrete truss and continuum topology optimization formulations. EPSRC (under grant number EP/N023471/1).

In this paper truss layout optimization is used in conjunction with geometry optimization to provide the basis for a powerful conceptual design tool for additively manufactured (AM) components, particularly useful when the degree of design freedom is high. With layout optimization the design domain is discretized using a grid of nodes which are interconnected with discrete line elements, forming a ‘ground structure’. Linear optimization can then be used to identify the subset of elements forming the minimum volume structure required to carry the applied loading. A nonlinear geometry optimization step, which involves adjusting the positions of the nodes, can subsequently be undertaken to simplify and improve the solution. Simple geometrical rules can then be used to automatically transform a line element layout into a 3D continuum, ready for validation and/or manufacture. Various extensions to the basic method are described in the paper, including AM build direction constraints and techniques to permit user-interaction with candidate designs, which has been found to be invaluable at the conceptual design stage. Finally the approach described is applied to a range of design problems, including the redesign of an airbrake hinge for the Bloodhound Supersonic Car.

In this study, the optimal layout of the principal structural members forming a building frame are sought, considering both gravity and lateral loads. The plastic design layout optimization formulation is used, considering the multiple load cases arising from the requirements of a well-known structural design code. The superposition approach is shown to be applicable to the three primary load case problems involved. It is found that the optimal layouts identified differ from those obtained when bracing is sought for a pre-existing frame, already designed to resist gravity loads. A significant finding is that a parameter related to the difference in vertical and lateral loads to be applied in the applicable load cases is a key factor determining the optimal layout of frame members. Since applicable load cases are design code dependent, this also indicates that optimal layout will be strongly influenced by choice of design code. Simple benchmark problems and a practical building design example are used to illustrate the concepts explored.

Truss layout optimization problems with global stability constraints are nonlinear and nonconvex and hence very challenging to solve, particularly when problems become large. In this paper, a relaxation of the nonlinear problem is modelled as a (linear) semidefinite programming problem for which we describe an efficient primal-dual interior point method capable of solving problems of a scale that would be prohibitively expensive to solve using standard methods. The proposed method exploits the sparse structure and low-rank property of the stiffness matrices involved, greatly reducing the computational effort required to process the associated linear systems. Moreover, an adaptive ‘member adding’ technique is employed which involves solving a sequence of much smaller problems, with the process ultimately converging on the solution for the original problem. Finally, a warm-start strategy is used when successive problems display sufficient similarity, leading to fewer interior point iterations being required. We perform several numerical experiments to show the efficiency of the method and discuss the status of the solutions obtained.

The 2014-16 outbreak of ebola virus disease (EVD) in West Africa resulted in 11,308 deaths. During the outbreak only 60% of patients were laboratory confirmed and global health authorities have identified the need for accurate and readily deployable molecular diagnostics as an important component of the ideal response to future outbreaks, to quickly identify and isolate patients. Areas covered: Currently PCR-based techniques and rapid diagnostic tests (RDTs) that detect antigens specific to EVD infections dominate the diagnostic landscape, but recent advances in biosensor technologies have led to novel approaches for the development of EVD diagnostics. This review summarises the literature and available performance data of currently available molecular diagnostics for ebolavirus, identifies knowledge gaps and maps out future priorities for research in this field. Expert opinion: While there are now a plethora of diagnostic tests for EVD at various stages of development, there is an acute need for studies to compare their clinical performance, but the sporadic nature of EVD outbreaks makes this extremely challenging, demanding pragmatic new modalities of research funding and ethical/institutional approval, to enable responsive research in outbreak settings. Retrospective head-to-head diagnostic comparisons could also be implemented using biobanked specimens, providing this can be done safely.

A 30-year-old G4P3 female was referred for evaluation of diabetes during her third trimester of pregnancy. Her pre-pregnancy BMI was 22 kg/m2. She did not have a history of gestational diabetes during her three preceding pregnancies.

In this paper, we introduce geometry optimization into an existing topology optimization workflow for truss structures with global stability constraints, assuming a linear buckling analysis. The design variables are the cross-sectional areas of the bars and the coordinates of the joints. This makes the optimization problem formulations highly nonlinear and yields nonconvex semidefinite programming problems, for which there are limited available numerical solvers compared with other classes of optimization problems. We present problem instances of truss geometry and topology optimization with global stability constraints solved using a standard primal-dual interior point implementation. During the solution process, both the cross-sectional areas of the bars and the coordinates of the joints are concurrently optimized. Additionally, we apply adaptive optimization techniques to allow the joints to navigate larger move limits and to improve the quality of the optimal designs.

Author(s): Gilbert, Matthew | Abstract: This essay examines a scene from Lee Chang-dong’s film Burning (2018) as part of a larger discussion around class conflict. A Korean filmic adaptation of a short story originally by Japanese author Haruki Murakami, Burning tells the story of Jeong-su, a poor farmer who is caught in a love triangle with Hae-mi, an old classmate, and her new boyfriend, Ben, a mysterious, wealthy socialite. In a pivotal scene, Lee turns the camera on Hae-mi as she dances to a song by Miles Davis, creating a filmic parallel to Murakami’s liminal spaces and forcing the audience to question reality. Through a consideration of textual and paratextual material, I argue that the director Lee Chang-dong uses music and dance to critique toxic masculinity through subtle sound editing techniques and narrative and metaphorical signifiers of class and power. Ultimately, Lee breaks from the source material to simultaneously express and nullify Hae-mi’s agency and place her at the heart of the narrative.

Background: Isolated thoracolumbar vertebral transverse process fractures (TPF) are often considered a stable injury. However, the use of advanced imaging such as magnetic resonance imaging and spine specialist consultation are often ordered as part of the routine workup of these fractures. The routine ordering of advanced imaging, spine specialist consultation, and delayed mobilization causes unnecessary economic and clinical burdens to patients and the overall healthcare system. Purpose: To determine if a higher number of isolated TPFs (iTPFs) lead to an increase in ligamentous injury to the spine, and whether ligamentous injury—if present—requires surgical intervention. Methods: The retrospective review was performed from 2009 to 2015, using a surgical trauma database to identify patients with greater than 3 isolated TPF (iTPF) to determine if iTPF leads to an increase in ligamentous injury to the spine and if this increase leads to increased surgical intervention. Results: A total of 102 patients were identified with complete follow up at 6 - 8 weeks post injury. The majority of the included patients suffered from blunt trauma. There was a small rate of ligamentous injury (n = 7, 7%) that did not require additional treatment. None of the fractures included were considered unstable. None of the patients included required surgical intervention during their hospital visit or in follow up visits. Conclusion: iTPFs are a stable injury to the thoracolumbar spine. There is a small rate of associated ligamentous injury that does not change the management or require further interventions. Thoracolumbar iTPFs do not automatically need spine specialist consultation and advanced imaging techniques.

Limit analysis has been used for many years to rapidly estimate the ultimate load-carrying of masonry arch bridges. However, often only masonry elements are modelled directly, with the surrounding soil backfill modelled in a simplified, indirect, manner. Due to the importance of the soil backfill, this may lead to inaccurate predictions of the load-carrying capacity of a bridge. In this contribution, a soil backfill model based on lower-bound (stress field) theory is proposed, similar to that used to compute the bearing capacity of shallow foundations. In the model the Mohr-Coulomb criterion is strictly obeyed in the stress fields in the soil fill surrounding the masonry elements of bridge. The model is applied to backfilled masonry arch bridges, with results compared with the upper-bound (failure mechanism) solutions obtained using the discontinuity layout optimization (DLO) numerical limit analysis procedure.

Limit analysis provides a simple yet powerful and effective means of verifying the safety of masonry arch bridges. However, a disadvantage of traditional rigid block limit analysis methods is that any soil fill surrounding the arch barrel in a bridge cannot readily be modelled directly, since the locations of potential failure planes in the soil are not known in advance. Also, it will seldom be feasible to model every individual unit in the masonry parts of a bridge with a rigid block. In this contribution discontinuity layout optimization (DLO) is used to extend the scope of the traditional rigid block analysis method, enabling direct modelling of both masonry and soil elements. DLO involves discretizing a solid body using nodes, and then interconnecting pairs of nodes with potential failure plane discontinuities. Optimization can then be used to identify the critical subset of discontinuities at failure which defines the geometry of the critical failure mechanism. In this contribution DLO is applied to both soil and masonry problems before being applied to a number of representative masonry arch bridge problems.

Masonry arch bridges continue to form a vital part of the transport networks of the UK and other countries around the world, where most masonry arch bridges have typically been in service for well over 100 years. To verify that they can safely carry modern traffic they need to be regularly assessed; however, assessment is not always straightforward, due to the wide range of geometrical configurations encountered and the many variables that influence structural behaviour. Specifically, whereas research in recent years has predominantly focused on the behaviour of arch bridges containing soil backfill, much less attention has been paid to bridges containing internal spandrel walls, which have different performance characteristics. In the present study the discontinuity layout optimization (DLO) numerical limit analysis technique is applied to bridges incorporating internal and/or external spandrel walls. DLO is an upper bound method capable of modelling both soil and masonry elements, enabling comparisons to be drawn between the behaviour of bridges containing soil fill and internal spandrels. After first validating numerical results against laboratory masonry arch bridge tests, the method is applied to a field bridge containing internal spandrel walls.

Numerical layout optimization employing an adaptive `member adding' solution scheme provides a computationally efficient means of generating (near-)optimum trusses for problems involving single or multiple load cases. To encourage usage of the method, a Python script is presented, allowing medium to large-scale problems to be solved efficiently. As well as handling multiple load cases, the short (98 line) script presented can tackle truss optimization problems involving unequal limiting tensile and compressive stresses, joint costs, and non-convex polygonal domains, with or without holes. Various numerical examples are used to demonstrate the efficacy of the script presented.

The discontinuity layout optimization (DLO) numerical modelling procedure is used to model the slip-line fields associated with plastic deformation and chip formation in metal cutting operations. A series of orthogonal and oblique cutting operations at low and high cutting speeds are simulated, with modelling results validated against key cutting parameter data from machining trials (cutting forces, chip morphology etc.). Reasonably good correlation between the predicted and experimental outputs is obtained, suggesting that the DLO method may provide a viable alternative to traditional methods such as incremental finite element analysis.

Background: An estimated 10% of children and adolescents with chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) experience eating difficulties; however, little is known about why these difficulties develop, what the impact is or how to manage them. Methods: Semi-structured interviews were conducted with adolescents (aged 12–17 years) attending a specialist service who have a primary diagnosis of CFS/ME and experience nausea, abdominal pain and/or eating difficulties. A total of 11 adolescents were interviewed (eight female, mean age: 15 years). Transcripts were analysed thematically using techniques of constant comparison which commenced soon after data collection and informed further interview protocols. Results: Adolescents perceived their eating difficulties were caused by abdominal symptoms, being too fatigued to eat and changes to their senses of taste and smell. Some of the adolescents recognised how their eating difficulties were exacerbated and maintained by psychological factors of low mood and anxiety. The adolescents eating difficulties had a negative impact on their weight, fatigue, socialising and family life. They perceived helpful interventions to include modifying their diets, families adjusting and also medical interventions (e.g. medication). Adolescents identified that early education and support about diet and eating habits would have been helpful. Conclusions: If adolescents diagnosed with CFS/ME develop eating difficulties, this has a significant impact on their quality of life, illness and on their families. Not eating increases fatigue, low mood and anxiety which further exacerbates the eating difficulties. Clinicians should screen for eating difficulties in those with symptoms of nausea and abdominal pain, warn adolescents and their families of the risk of developing eating difficulties and provide interventions and support as early as possible.

Additive manufacturing (‘3D printing’) techniques provide engineers with unprecedented design freedoms, opening up the possibility for stronger and lighter component designs. In this paper ‘layout optimization’ is used to provide a reference volume and to identify potential design topologies for a given component, providing a useful alternative to continuum based topology optimization approaches (which normally require labour intensive post-processing in order to realise a practical component). Here simple rules are used to automatically transform a line structure layout into a 3D continuum. Two examples are considered: (i) a simple beam component subject to three-point bending; (ii) a more complex air-brake hinge component, designed for the Bloodhound supersonic car. These components were successfully additively manufactured using titanium Ti-6Al-4V, using the Electron Beam Melting (EBM) process. Also, to verify the efficacy of the process and the mechanical performance of the fabricated specimens, a total of 12 beam samples were load tested to failure, demonstrating that the target design load could successfully be met.

Discontinuity layout optimisation (DLO) is a generally applicable numerical limit analysis procedure that can be used to identify critical plastic collapse mechanisms in engineering problems. Considering the modelling of in-plane failure, the authors have previously presented a formulation capable of identifying rotational failure mechanisms in non-dilating media. However, the formulation presented did not explicitly address cases involving confined geometries, where curved slip lines could potentially intersect boundaries. In this paper, methods are outlined which permit efficient modelling of such cases. Details of the kinematic and equilibrium formulations are provided, which are then verified through application to various geotechnical and structural mechanics problems. It is shown that results of high accuracy can be obtained, both in terms of the predicted collapse load and the corresponding failure mechanism.

Grillages are often used to form bridge decks and\ud other constructions. However, following a period of intensive\ud research activity in the 1970s, comparatively little attention\ud has been paid to optimizing the layout of grillages in\ud recent years. In this contribution a new numerical procedure\ud is proposed which takes advantage of the adaptive solution\ud scheme previously developed for truss layout optimization\ud problems, enabling very large scale problems to be solved.\ud A key benefit of the proposed numerical procedure is that it\ud is completely general, and can therefore be applied to problems\ud with arbitrary loading and boundary conditions. Also,\ud unlike some previously proposed procedures, the sizes of\ud individual beams can readily be discerned. To demonstrate\ud its efficacy the numerical procedure is applied to a range of\ud grillage layout design problems, including load dependent\ud problems which could not be solved using traditional methods.\ud It is shown that important phenomena such as “beamweaves”\ud can be faithfully captured and new high-precision\ud numerical benchmark solutions are provided.

Bracing is commonly used to provide resistance to lateral forces in building structures. However, traditional bracing design approaches appear not to be underpinned by clear fundamental principles. Here, theoretically optimal arrangements of bracing members are sought for pre-existing building frames, already designed to carry gravity loads. For sake of simplicity existing frame elements are assumed to be capable of carrying additional loads and three types of bracing are considered: tension only bracing, bracing intersecting only at the corners of the existing frame, and unconstrained optimal bracing, where bracing elements can intersect at any location. Layout optimization techniques are used to identify initial design solutions; these are then related to Michell trusses to obtain exact reference volumes, against which the efficiency of other bracing layouts can be judged. It is shown that from a theoretical standpoint tension only bracing is inefficient and that the optimal angle of intersection between a pre-existing frame member and intersecting tension/compression bracing member pairs is 45 ∘ , something that can potentially be adopted as a basic principle when designing bracing for a pre-existing frame.

Masonry arch bridges are found in large numbers on the rail networks of Europe and other parts of the world. However, the mode of response of masonry arch structures subjected to railway loading is little understood. To address this, an experimental study involving large-scale physical models of backfilled masonry arch bridges subjected to railway loading conditions has recently been conducted. This has explored the influence of the rail track bed system on bridge behaviour and on load carrying capacity. Tests indicate that the track bed system fundamentally alters the mode of response of the bridge system, and significantly increases load carrying capacity. Using the same test facility, load tests have also been used to explore and characterise the behaviour and performance of damaged arch bridges, with the test results obtained suggesting that although there is likely to be a reduction in overall capacity, even a significantly damaged arch bridge can still perform adequately under loading. This has important implications for bridge owners and assessment engineers.\ud \ud Keywords: masonry arch bridges, physical modelling, cyclic loading, rail track system, backfill.

Numerical truss layout optimization employs a ground structure which comprises a large number of potential structural elements from which an optimal subset is sought. The basic problem formulation can be solved via linear programming, which means that very large problems can be solved quickly. However, although layout optimization has been found to provide a highly effective means of identifying (near-)optimal truss layouts, these can be overly complex in form and hence unsuitable for practical use. To address this, a range of practical considerations can potentially be incorporated in layout optimization formulations directly (e.g. via the inclusion of nonlinear and/or nonsmooth terms). However, this will often greatly increase computational cost. Also, some practically important constraints are difficult to specify mathematically (e.g. aesthetic considerations). Furthermore, rather than being presented with a single ‘optimal’ design, designers often seek more flexible tools that allow them to interactively modify a design for a wide range of reasons.

This paper presents a new half-plane Michell structure that transmits a uniformly distributed load of infinite horizontal extent to a series of equally-spaced pinned supports. A full kinematic description of the structure is obtained for the case when the maximum allowable tensile stress is greater than or equal to the allowable compressive stress. Although formal proof of optimality of the solution presented is not yet available, the proposed analytical solution is supported by substantial numerical evidence, involving the solution of problems with in excess of 10 billion potential members. Furthermore, numerical solutions for various combinations of unequal allowable stresses suggest the existence of a family of related, simple, and practically relevant structures, which range in form from a Hemp-type arch with vertical hangers to a structure which strongly resembles a cable-stayed bridge.