Current Design Procedures Research Articles

Effect of Earthquakes on Some Kind of Buildings

A new method that simplifies the current static seismic torsion design procedure for buildings is proposed. Distribution of the shear forces among the storey-resistant elements designed by torsion and of the factors which affect the design eccentricity, specially accidental eccentricity, are studied. It is demonstrated that the effect of accidental eccentricity is always additive for the structural elements. There is given an in which the proposed procedure is applied; the results obtained agree with those calculated obtained with a traditional procedure of design.

Structural Capacity of Rammed Earth in Compression

Rammed earth walls are formed by compacting subsoil in thin layers inside temporary supporting formwork. An ancient form of construction, rammed earth has in recent years, together with other earth building methods, been increasingly used structurally in a range of contemporary buildings in many countries around the world. Though current structural design procedures for earth walls, including rammed earth, in general use provisions based on structural masonry standards, this approach has never been satisfactorily validated. This paper presents experimental results from material and large-scale testing and develops a simple theoretical model, applied to rammed earth columns subject to concentric and eccentric axial compression loading. An analytical model, using a basic strut theory, shows favorable correlation with the experimental results for all load eccentricities.

A new tuning procedure for the DTL RF field pattern

The DTL tank is a multi-cell cavity. In a fabricated tank, the measured average axial field E0 for each cell may obviously deviate from the designed value. It is generally thought the deviation is due to the errors in fabrication and assembly. But it is not always true. In this paper, it is shown that the deviation may already exist before fabrication in some cases. It is partly due to the imperfection of the current design procedures. A new design method is introduced to reduce the deviation in the design stage.

Seismic performance of composite moment-resisting frames

This paper examines the seismic performance of composite steel–concrete moment-resisting frames. A number of studies are carried out in order to assess the influence of key parameters, related to the structural configuration as well as design and loading considerations, on the inelastic seismic behaviour. Several sensitivity and parametric investigations are undertaken using an advanced analysis program that accounts for material and geometric nonlinearities. Particular emphasis is given to composite frames designed according to the provisions of the European seismic code, Eurocode 8. The validity of employing simplified nonlinear-static loading approaches is evaluated by comparison against the results of incremental dynamic time-history analysis. Natural earthquake acceleration records, which are specifically selected and adjusted for compatibility with the adopted design spectrum, are utilised for this purpose. In terms of frame configuration, it is shown that the span of the composite beam, the extent of gravity loading and the number of stories can all have significant implications on the actual inelastic response characteristics of the structure. Moreover, several design assumptions and decisions, such as those related to the behaviour factors, drift considerations, moment redistribution and panel zone contribution, can also have a direct impact on the resulting performance. The studies presented in this paper highlight important behavioural observations and trends, some of which point towards the need for further consideration and refinement of current design procedures.

Earthquake Shear Load in Load-Bearing Masonry Buildings

Load-bearing masonry buildings are composed of concrete slabs and supporting masonry walls, and in Australia usually incorporate slip joints in the interfaces between walls and slabs for serviceability reasons. The apparent conflicting requirements of the slip joints, to slip under long-term loads and to transmit short-term loading from wind and earthquake actions, together with the lack of attention to the design of slip joints, make slip in the joints likely to occur when the building is subjected to a lateral loading. Joint slip leads to a redistribution of loading in the building wall system, resulting in wall shear loads different from that determined using the current standard elastic design procedures. Redistribution of loading may be also caused by softening of the masonry. This paper has assessed the realistic response of various load-bearing masonry buildings, including the potential for slip in the joints and softening of the masonry, and evaluated the level of wall shear load deviations resulting from the application of current design procedures. Analyses of the buildings, using non-linear static and dynamic finite element models, have indicated that joint slip may occur in buildings subjected to earthquake loading. The application of current elastic design procedures, which do not account for loading redistribution, resulted in major wall shear load deviations, such as overestimations of up to +75% and underestimations of up to-62%. It was therefore concluded that improvements in the current design procedures are required for a more accurate evaluation of wall shear loads in load-bearing masonry buildings subjected to the lateral loading.

Where is Shear Reinforcement Required? Review of Research Results and Design Procedures

This paper presents a review of research on shear strength of reinforced concrete members without stirrups (shear reinforcement). A database of 1849 available experimental results from over the past 60 years is examined and these results are compared to predictions from current North American shear design procedures. Special attention is paid to the behavior of beams ranging from short span deep beams to members controlled by flexure. The findings from the review indicate that using the current ACI shear provisions to decide where shear reinforcement is required can be unconservative for members with larger effective depths, or higher stresses in the longitudinal reinforcement. Improvements to the ACI Code are proposed to mitigate these weaknesses. The AASHTO-LRFD and Canadian CSA sectional and strut-and-tie provisions are found to provide a more uniform level of safety for all member types. The results from this review can allow engineers to identify members in their own structure where a more conservative shear design procedure is appropriate.

Numerical analysis of reinforced soil-retaining wall structures with cohesive and granular backfills

The failure mechanisms of reinforced soil segmental walls with extensible reinforcements were studied by performing a numerical analysis using the finite element method. The numerical approach was first verified against the results of three instrumented full-scale structures reported in the literature. Finite element models with different combinations of reinforcement spacing, reinforcement length and backfill soil were analysed. The ϕ–c reduction method, which is a special shear strength parameter reduction technique, was applied to simulate the failure conditions. The results of ϕ–c reduction analysis were used to evaluate assumptions used in current design procedures for geosynthetic-reinforced soil walls. In particular, shear strains were used to identify failure surfaces. Interpretation of the results indicated that, for both granular and cohesive backfills, the potential failure surface gradually shifts to a direct sliding mode as the system approaches failure. As a result, under working loads the potential failure surface used in current design analysis is correct, but the failure plane of a geosynthetic-reinforced soil-retaining wall at failure approaches a direct sliding type or a bilinear plane, which starts from the toe of the wall with a very shallow slope.

Prediction of Resilient Modulus of Cohesive Subgrade Soils from Dynamic Cone Penetrometer Test Parameters

Current pavement design procedures recommend the resilient modulus of subgrade materials for pavement design and analysis. The objective of this paper is to develop two statistical models to predict the resilient modulus of subgrade cohesive soils from the dynamic cone penetration (DCP) test parameters and soil properties. The first model correlates resilient modulus to the dynamic cone penetration test parameters, while the second model correlates resilient modulus to both the dynamic cone penetration test parameters and soil properties. Field and laboratory experiments were conducted at 31 sites in Louisiana that contain four common soil types (A-4, A-6, A-7-5, and A-7-6). Field tests included DCP tests and soil sampling, while laboratory tests included determining basic soil properties and resilient modulus. Statistical analyses were conducted on the collected data, and two statistical models were developed for the prediction of resilient modulus of cohesive subgrade soils from the DCP test parameters and soil properties. The models predicted a separate data set that was not used in their development, indicating the success of the application of the dynamic cone penetration test in evaluating the resilient modulus of pavement subgrade soils. The predicted values obtained from the proposed models corresponded well with the measured resilient modulus values from the repeated load triaxial test.

Shear Design of Prestressed Concrete: A Unified Approach

Design methods for the shear resistance of reinforced and prestressed concrete beams are based on empirical evidence. Due to different approaches in their development, different equations are used to calculate the shear strength of reinforced and prestressed concrete. Recent research has provided a simplified approach for the shear design of reinforced concrete that eliminates many of the shortcomings of current design procedures and corresponds well to a wide range of test results. The objective of this research was to investigate the applicability of this new approach to prestressed concrete. The applicability of the shear model was evaluated by a comparison of its results with the experimental strengths of 86 specimens which failed in shear. This investigation indicated that the shear model is applicable to prestressed sections. For design purposes, the shear model was simplified to develop a design expression that unifies the design of reinforced and prestressed concrete sections.

Fracture Moment Strength of Reduced Beam Section with Bolted Web Connections

Reduced Beam Section (RBS) moment connections are developed for Special Moment Resisting Frames (SMRF). According to the beam web attachment the column flange RBS connections are classified into Reduced Beam Section with Bolted web connections (RBS-B), and the Reduced Beam Section with Welded web connections (RBS-W). Beam flanges are welded to the column. Regardless of different web attachment details in RBS-B and RBS-W connections current design procedures (FEMA 350) assumes that they could develop plastic moment of the beam gross section. In current design procedures, RBS-B connections should provide the sufficient strength that can reach the plastic moment capacity of the connected beam. However, some experimental researches reported that the beams in RBS-B connections fractured before the connection reached its plastic moment capacity. Such undesirable fracture shows that RBS-B connections have less strength than RBS-W connections. And if RBS-B connections designed in current design procedures, it might fail in a brittle manner and not satisfy SMRF due to undesirable fracture. Thus, this study develops a new set of equations for accurately computing the moment strength of RBS-B connections. The proposed strength equation accurately predicts connection moment capacity for RBS-B connections.

The dynamic shear capacity of concrete structures

For shear capacity, the current design procedure used for concrete structures has been found to be inaccurate for some dynamic design load cases. Loads traditionally believed to be highly dynamic are only within the quasi-static range, but it is known that the combination of a high impact velocity and a hard, stiff impact will lead to shear failure. Load cases on concrete structures which can be classified as dynamic are, for example, those relating to weapons and hard impacts from steel objects. The characteristic of a dynamic load has great influence on the overall response and mode of failure of concrete structures. When structures which have been designed to fail in flexure under static loads fail in shear when loaded dynamically, the reason is probably the changing frequency content of the load. On the basis of a literature review, some important conclusions and recommendations are presented in this paper. The results will be used in further evaluation of existing design tools, aiming at accurate and reliable routines for the design of safe and cost-efficient concrete structures.

Exhaustive Mutagenesis of Six Secondary Active-Site Residues in Escherichia coli Chorismate Mutase Shows the Importance of Hydrophobic Side Chains and a Helix N-Capping Position for Stability and Catalysis

Secondary active-site residues in enzymes, including hydrophobic amino acids, may contribute to catalysis through critical interactions that position the reacting molecule, organize hydrogen-bonding residues, and define the electrostatic environment of the active site. To ascertain the tolerance of an important model enzyme to mutation of active-site residues that do not directly hydrogen bond with the reacting molecule, all 19 possible amino acid substitutions were investigated in six positions of the engineered chorismate mutase domain of the Escherichia coli chorismate mutase-prephenate dehydratase. The six secondary active-site residues were selected to clarify results of a previous test of computational enzyme design procedures. Five of the positions encode hydrophobic side chains in the wild-type enzyme, and one forms a helix N-capping interaction as well as a salt bridge with a catalytically essential residue. Each mutant was evaluated for its ability to complement an auxotrophic chorismate mutase deletion strain. Kinetic parameters and thermal stabilities were measured for variants with in vivo activity. Altogether, we find that the enzyme tolerated 34% of the 114 possible substitutions, with a few mutations leading to increases in the catalytic efficiency of the enzyme. The results show the importance of secondary amino acid residues in determining enzymatic activity, and they point to strengths and weaknesses in current computational enzyme design procedures.

Evaluation of Seasonal and Yearly Behavior of an Integral Abutment Bridge

This paper presents the field performance evaluation of an integral abutment bridge constructed in Massachusetts that was monitored for a period of three years. Emphasis is primarily made on observed seasonal and yearly behavior. Although the bridge abutments were constructed without any skew, differences have been observed in performance between the north and south abutments and are attributed to differences in construction conditions. Longitudinal displacement and rotation fully characterize the abutment deformation response. Fundamental parameters that control the response of the bridge (longitudinal restraint, pile moments) are evaluated through the use of simple mechanical models. The use of simple models allows estimation of bridge parameters for use in more involved finite element models. Data collected during the monitoring period indicate that current design procedures used for integral abutment bridges in Massachusetts are conservative.

Simultaneous Prediction of Saturated Hydraulic Conductivity and Drainable Porosity Using the Inverse Problem Technique

The saturated hydraulic conductivity K and the effective porosity f are two important input parameters needed for lateral drain spacing design, as well as some other applications. The technical and economic justification, of most drainage projects, is mainly connected to these two parameters. The current design procedure is based upon calculation of the lateral spacing, using some average values of K and f within the drainage area. The objectives of this study were to introduce a new method for simultaneous estimation of K and f parameters using the inverse problem technique, and to evaluate five different unsteady drainage analytical models of the Boussinesq equation, suggested by different researchers for simultaneous prediction of the parameters. Consequently, five different analytical models for predicting water table profiles were solved, using the inverse problem technique. Each model was then evaluated. A physical drainage model of 2.2 m length, 0.3 m width, and 0.5 m height was established in the ...

L-Spandrels: Can Torsional Distress Be Induced by Eccentric Vertical Loading?

Current code-required design procedures for eccentrically loaded L-spandrels assume that torsional distress is the mode of failure at ultimate shear-torsion capacity and prescribe appropriate reinforcement to accommodate such distress. The more commonly accepted design procedures vary in complexity, but all result in the need for heavy reinforcement and complex detailing that are expensive with regard to both material and fabrication labor costs. Based on observation of the failure mode of an L-beam in a full-scale torsion test conducted by the author in 1961, and particularly on his diagnosis of the failure modes of L-spandrels in tests conducted in the mid-1980s by Wiss, Janney, Elstner Associates Inc., the author concludes that the face shell spalling and severe spiral cracking associated with torsional distress is not induced in L-spandrels at ultimate failure by eccentric vertical loading. Thus, the current complex design procedures and the complexity and expense of reinforcement resulting from these procedures are not justified. Instead, the ultimate capacity in the end region of L-spandrels is satisfied by the reinforcement required in their inside face to resist out-of-plane bending. Concrete shear capacity is checked by the V CW equation and seldom requires additional reinforcement in deep L-spandrels.

Probabilistic procedure for design of untreated timber piles under marine borer attack

This paper presents a probabilistic design procedure for untreated timber piles under attack of marine borers, in which a new probabilistic-based durability factor is derived and introduced into the current Australian engineering design procedure. In evaluating this durability factor, a prediction model of marine borer attack on timber piles, which was developed in a national project in Australia is used for modeling the attack progress. Examples of the durability factor computed for untreated timber piles with different diameters or located at different coastal zones are provided.

Cyclic Load Behavior of Reinforced Concrete Beam-Column Subassemblages of Modern Structures

The beam-to-column connection and columns in ductile moment-resisting frames must remain essentially elastic throughout the load history to ensure the lateral stability of the structure. This study examines the seismic performance of 4 one-half scale exterior beam-column subassemblages subjected to a large number of cyclic lateral loads to approximate severe earthquake damage. All subassemblages were typical of new structures and incorporated full seismic details from current Eurocode, American Concrete Institute and Greek building codes, such as a weak girder-strong column design philosophy. Results from the cyclic load tests indicate that provisions related to the design of beam-column joints in several of the codes investigated appear to need improvement. Current design procedures could sometimes result in excessive damage to the joint regions and the columns' critical regions. This can lead to premature lateral instability in ductile moment-resisting frames of modern structures.

Three-Dimensional Cyclic Behavior Simulation of RC Columns under Combined Flexural Moment and Torsion Coupled with Axial and Shear Forces

Full three-dimensional nonlinear finite element analysis based on the path-dependent non-orthogonal multi-directional crack model is applied to RC columns subjected to combined cyclic flexure/shear and torsion. This loading causes non-orthogonal crack-to-crack mechanistic interactions accompanying opening/closure and shear slip along crack planes. The analytical results show that the proposed methodology is able to simulate the highly nonlinear behavior of RC columns under cyclic loading, including not only load-carrying capacity but also complex restoring force characteristics and post-peak softening after peak strength. Sensitivity analysis is also carried out to examine the effectiveness of the transverse reinforcement, which simultaneously resists both transverse shear and torque moment. The current design procedure for determining the necessary and sufficient amount of web reinforcement is reviewed and the necessity of performance assessment is raised.

Seismic Design Criteria for Slab-Column Connections

Two-way slabs without beams are popular floor systems because of their relatively simple formwork and the potential for shorter story heights. Earthquakes, however, have demonstrated that slab-column frames are vulnerable to brittle punching shear failures in the slab-column connection region and dropping of the slab, which are costly to repair. This paper focuses on the behavior and design of slab-column connections under combined gravity and lateral loading and reviews current design procedures, performance-based design approaches, and relevant experimental data. An equation relating the gravity shear ratio at a slab-column connection to drift capacity is presented. Finally, practical recommendations are provided for defining specific performance objectives.

Reply to Discussion by S. Chen on "Strengthening precast-prestressed hollow core slabs to resist negative moments using carbon fibre reinforced polymer strips: an experimental investigation and a critical review of Canadian Standards Association 806-02"

The authors would like to thank the discusser for his valuable discussion and will present their reply in the following sections. We appreciate, and totally agree with the discusser’s opinion that a similar approach to the technique presented in this investigation may also be applied in repairing or upgrading existing damaged precast concrete (PC) and reinforced concrete (RC) slabs in buildings. The proposed approach in our work that implements a new debonding model (Teng et al. 2002) into the current design procedures improves the current practice and gets the experimental results closer to predictions of codes of practice such as Canadian Standards Association (CSA) standard CSA-S806-02 (CSA 2002, Hosny et al. 2006a) and American Concrete Institute (ACI) standard ACI 440.2R-02 (ACI 2002, Hosny et al. 2006b). However, and despite this improvement, we still consider that our proposed method does not show a perfect agreement with the experimental results and still needs further fine tuning to its parameters as mentioned in Hosny et al. (2006a). Currently, an experimental and numerical investigation is on-going to achieve this goal. Cracking moments of control slabs