How do complex adaptive systems, such as life, emerge from simple constituent parts? In the 1990s, Walter Fontana and Leo Buss proposed a novel modeling approach to this question, based on a formal model of computation known as the λ calculus. The model demonstrated how simple rules, embedded in a combinatorially large space of possibilities, could yield complex, dynamically stable organizations, reminiscent of biochemical reaction networks. Here, we revisit this classic model, called AlChemy, which has been understudied over the past 30 years. We reproduce the original results and study the robustness of those results using the greater computing resources available today. Our analysis reveals several unanticipated features of the system, demonstrating a surprising mix of dynamical robustness and fragility. Specifically, we find that complex, stable organizations emerge more frequently than previously expected, that these organizations are robust against collapse into trivial fixed points, but that these stable organizations cannot be easily combined into higher order entities. We also study the role played by the random generators used in the model, characterizing the initial distribution of objects produced by two random expression generators, and their consequences on the results. Finally, we provide a constructive proof that shows how an extension of the model, based on the typed λ calculus, could simulate transitions between arbitrary states in any possible chemical reaction network, thus indicating a concrete connection between AlChemy and chemical reaction networks. We conclude with a discussion of possible applications of AlChemy to self-organization in modern programming languages and quantitative approaches to the origin of life.

The utilization of Ultra-High-Performance Concrete (UHPC) for connecting bridge elements in accelerated bridge construction has become increasingly prevalent. Among their various applications, connecting bridge decks using UHPC stands out due to its ability to leverage key properties, including enhanced shear strength, tensile strength, compressive strength, and fatigue resistance. This study focuses on extensive testing and material modeling using an approach to use the flexural test results of small beams for back-calculation and validation of material constitutive response and using these properties in the context of a hybrid reinforcement strategy for typical UHPC bridge deck connection elements. Experimental programs were conducted using a 4-point bend test at both the materials and structural levels. After the assessment of the material data obtained from closed-loop tests, the results were evaluated using an actual-size reinforced concrete section tested under flexure. Results reveal multiple cracking mechanisms induced by the fibers, with the fibers exhibiting substantial capacity to withstand loads at large deflections. The analysis was used to characterize the contribution of the matrix, fiber, and reinforcement rates, thus providing insight into the tension-stiffening behavior of Hybrid section composites.

Precast tunnel lining segments manufactured with synthetic macro-fibers and steel fibers as the primary reinforcement were tested under flexural and edge compression loading. Since steel fibers are usually prescribed as the primary reinforcement of tunnel sections, the dosage of synthetic fibers was determined by matching their residual flexural strength. The performance of tunnel segments was verified using the extensive data collected from instrumented deflection, crack growth, quantitative DIC, and strain gauge results and correlated with the load vs. deformation response. Results show that synthetic fibers can meet the design load requirements specified for the steel fibers reinforcement. Flexural test results indicate a 16% increase in macro-fiber content from 0.80% to 0.93% by weight resulting in a 32% increase in the residual strength of standard beam samples and a 41% increase in the residual strength of full sections. Compared to the steel fiber samples, samples with polymeric macro-fiber had a 6.5% higher average toughness. The full-scale load-deflection results were within 7% of the average values in each category of samples which is almost half the variation in the flexural ASTM C1609 results. The edge compression tests indicated that the mode of failure under concentrated jack forces is governed and dominated by the tensile lateral bursting stresses resulting from inefficient distribution of the load to the supporting edge.

A paradigm shift is proposed for the design of sustainable structures using UHPC. Using a combination of new materials formulations, and closed-form analysis procedures to calculate the load-deflection response of a structure, limit-state designs aimed at the long-term durability of cement composite systems are proposed. The perspective is to meet the traditional ultimate design criteria and emphasize the perspective on serviceability measures defined in terms of durability, deflection, stiffness, and performance aspects under the service loads. Three main stages of sustainable product development will be addressed using the material properties of non-proprietary UHPC. The influence of fiber type, matrix modifications, and processing parameters under tensile and flexural loading are incorporated in constitutive material properties. The enhanced tensile behavior in the post-cracking stage is primarily governed by mechanical anchorage and bond characteristics between matrix and fibers. The residual strength under flexural loads, allows for the distribution of localization and results in additional cracking. The significant delays in stiffness loss and damage localization allows for deflection hardening applications. Innovative methods of the combinations of steel and FRP rebar and fibers as well as different UHPC materials and measurement of characteristic material properties are presented. Results are compared with a variety of test results published.

Fiber reinforcement in precast tunnel segments is quite attractive since it reduces the cost and labor associated with the fabrication process while it improves the post-cracking behavior considerably. Among the benefits, one can address improvements in handling, fatigue, impact resistance and durability while reducing the crack widths significantly. Flexural tests of full-scale precast tunnel segments are conducted using a newly developed testing laboratory for large structural testing. Using the closed-form material properties obtained from the flexural beam specimens, the response of full sections is predicted and the test results are compared with the full-scale test results obtained on the testing facility. Using the proposed methodologies, one can develop proper material and structural models for the accurate design of tunnel segments due to their unique design characteristics.

Statistical process control procedures are widely applied to improve the production efficiency of industrial products. Application of quality control procedures in monitoring the production, delivery, and construction process are essential, especially when the historical data collected on various projects can be used to gain better insight to the operational procedures. Such information will promote interaction; reduce the liabilities and benefits the owners and suppliers if any of the design parameters that are below the minimum requirement can be identified as soon as possible. The longer time it takes to detect discrepancies in the data, the more the penalty, project delays, and the higher the associated costs to the owners and suppliers. A detailed analysis of the test results of flexural closed-loop control test data conducted in accordance to ASTMC1609 test is conducted for QC requirements of precast segment in tunnel lining project. More than 378 production samples are recorded. The data set contained 1 day (demolding age) and 28 days of molding. The statistical process control and the range of the data are studied in the context of material properties as well as back-calculation of the tensile parameters. The number of parameters evaluated includes flexural strength and deflection at ultimate flexural strength, the residual strength results at L/600, L/300 and L/150. A series of statistical analysis procedures to analyze the correlation of the parameters and addressed the combination of control charts for early detection of spurious shifts in the mean of the test data (out-of-control signal).