W. P. S. Dias

Mechanical Properties of Hardened Cement Paste Exposed to Temperatures up to 700 C (1292 F)

Temperatures of significance are identified in the range 20 to 700 C (68 to 1292 F) for changes in strength and elastic modulus both static and dynamic) of unsealed hardened cement paste measured at the various temperaturues as well as after cooling. These changes are correlated with chemical microstructural changes reported in the literature. The beneficial effects of thermal drying and loading, within limits, upon these mechanical properties are observed. It is concluded that these properties are dependent primarily on the maximum temperature of exposure as opposed to the temperature at testing.

Neural networks for predicting properties of concretes with admixtures

Abstract Backpropagation neural networks were used to predict the strength and slump of ready mixed concrete and high strength concrete, in which chemical admixtures and/or mineral additives were used. Although various data transforms were tried, it was found that models based on raw data gave the best results. When non-dimensional ratios were used, arranging the ratios such that their changes resulted in corresponding changes in the output (e.g. increases in ratios to cause increases in output values) improved network performance. The neural network models also performed better than the multiple regression ones, especially in reducing the scatter of predictions. Problems associated with models trained on non-dimensional ratios were uncovered when sensitivity analyses were carried out. A rational approach was used for carrying out sensitivity analyses on these mix design problems by constraining the sum of input values. These analyses, using the raw data based model, showed that the modelling had picked up not only the fundamental domain rules governing concrete strength, but also some well-known second order effects.

Reduction of concrete sorptivity with age through carbonation

Ordinary Portland cement (OPC) concrete specimens that had been air-dried for 3.5 years were found to have an increase in weight and reduction in sorptivity, with weight and sorptivity changes being greater for specimens with higher original sorptivity. Since this was attributed to carbonation of the surface zone, the porosity differences between end slices and the specimen interior in cylindrical specimens from another test series (of 4 years of age) were measured, together with the depths of carbonation. It was found from sensitivity analyses performed on a neural network model that the porosity difference can be attributed, in increasing order of importance, to (i) depth of carbonation, (ii) original sorptivity (which reflects both the quality of the mix and the efficiency of curing), and (iii) whether the end slice was a top or bottom one (reflecting the direction of casting and compaction). Tests on existing structures also showed that sorptivity decreased with age and also that (carbonated) surface sorptivities were lower than interior sorptivities, further confirming that the reduction of sorptivity with age is due to surface carbonation and that this carbonation occurs in and benefits surfaces with poorer initial quality more. This implies that carbonation could have mutually compensatory effects on some aspects of concrete durability.

Tsunami vulnerability functions from field surveys and Monte Carlo simulation

Data on tsunami damaged houses, collected and compiled by the Department of Census and Statistics, Sri Lanka, was used to construct vulnerability curves with tsunami height as the demand parameter. A common curve could be used for all administrative divisions where a majority of houses had permanent walling materials, whether these divisions were on the southwest coast or the north and east coast. A Monte Carlo simulation was carried out for a typical building using varying tsunami inundation depths, and the resulting vulnerability curve was found to be similar, but lie just below, the survey-based curve, because all the buildings used for the simulated curve had permanent walling materials. This paper focuses only on the ‘complete damage’ state for vulnerability.

The Integration of Product and Process Models for Design

Abstract A structural correspondence is demostrated between product and process models through the definition of generic units, called roles. Relationships and communication between roles are discussed as are the types of knowledge required for design. The blackboard and prototype frameworks are presented as implementation strategies that could integrate product and process models for design.

Philosophical grounding and computational formalization for practice based engineering knowledge

Michael Polanyis idea of tacit knowing and Martin Heideggers concept of pre-theoretical shared practice are presented as providing a strong rationale for the notion of practice based knowledge. Artificial Intelligence (AI) approaches such as Artificial Neural Networks (ANN), Case Based Reasoning (CBR) and Grounded Theory (with Interval Probability Theory) are able to model these philosophical concepts related to practice based knowledge. The AI techniques appropriate for modeling Polanyis and Heideggers ideas should be founded more on a connectionist rather than a cognitivist paradigm. Examples from engineering practice are used to demonstrate how the above techniques can capture, structure and make available such knowledge to practitioners.

SHRINKAGE OF HARDENED CEMENT PASTE AT TEMPERATURES UP TO 670 C (1238 F)

The transient and ultimate shrinkage behavior of unsealed hardened cement paste of water-cement ration (w/c)=0.3 was investigated for maximum exposure temperatures up to 670 C (1238 F) and a heating rate of 1 C/min (1.8 F/min). The shrinkage phase, the duration of which was dependent on the maximum exposure temperature, was modeled mathematically using a combined logarithmic and exponential expression. The amount of shrinkage experienced and the temperature at which the trend of increasing ultimate shrinkage is reversed was found to depend on the w/c ratio.

Dimensions of order in engineering design organizations

Abstract Design practice and artifacts in engineering design organizations can be ordered along four orthogonal dimensions, namely (i) the principle of ordering (top down vs bottom up), (ii) the structure of ordering (aggregation-decomposition vs generalization-specialization), (iii) the breadth of ordering (diversity vs parsimony) and (iv) the perspective of ordering (horizontal vs historical). Four case histories of design organizations are used to illustrate the above and also to demonstrate the tension (either in conjunction or in cyclic sequence) and/or balance between the extremes of the above dimensions. Mechanisms for creating a balance or tension between bottom up generation and top down influence are proposed.

SOFT SYSTEMS APPROACHES FOR ANALYSING PROPOSED CHANGE AND STAKEHOLDER RESPONSE - A CASE STUDY

Abstract This paper describes the use of soft systems approaches for analysing the changes envisaged in the course of proposing alternatives for river sand, used as a fine aggregate in the Sri Lankan construction industry. The use of hierarchical structuring of the change process for identifying general trends and emergent characteristics is described, as is the CATWOE method for listing features, issues and stakeholders associated with the various changes. The paper also gives a brief summary of the findings from the actual study on alternatives for river sand. It then describes a simple fuzzy set technique for ana lysing responses from stakeholders regarding the above changes, so that a composite qualitative response can be defined from a set of individual qualitative responses in the form of linguistic labels.

CONFAULT-AN EXPERT SYSTEM FOR FAULT DIAGNOSIS IN REINFORCED CONCRETE STRUCTURES

Abstract Diagnostic applications are especially suitable for expert systems. The expert system CONFAULT diagnoses faults in reinforced concrete structures by identifying fault sub types. The knowledge base in CONFAULT is divided into modules corresponding to six major fault types, while meta rules are used to control and limit searching. A modified confidence factor approach is used to deal with uncertainty.