Practice Periodical on Structural Design and Construction

Experimental investigations reported in the literature have shown that pile foundations exhibit nonlinear behavior when subject to dynamic axial service loads. The nonlinear characteristics are attributed to soil remolding, soil nonlinearity, and pile–soil separation/slippage. The traditional methodology for computing the nonlinear dynamic response of pile foundations requires the estimation of upward of six parameters pertaining to an inner annular region of weakened soil. This article presents a simplified approach to account for such nonlinear behavior of driven piles by introducing shear-moduli modification factors within the traditional elastic model. The proposed methodology, termed the modified elastic model, is computationally simpler than the traditional nonlinear model and requires significantly fewer parameter estimates. The modified elastic model is validated with nine experimental response curves originating from three test configurations.

This article focuses on elastic stability analysis of battened columns and laced columns with crosswise, fir-shaped, and serpentine lattices. The columns are considered as static indeterminate systems. The buckling problem of the column is formulated as a two-point boundary-value problem for a system of recurrence relations between displacements of the column joint nodes. For columns with any degree of static indeterminacy, the Euler buckling load is determined as the least eigenvalue of the fourth-order system of homogeneous linear algebraic equations. A buckling-mode shape of the column is displayed as a superposition of the set of displacements of the column joint nodes and the curves describing the deflection of the column chords between the joint nodes. Two different combinations of the end boundary conditions are considered. The Euler buckling load of the laced columns depends significantly on the rigidity parameters of the column lacings, and the Euler buckling load of the battened column depends on the rigidity parameters of the batten plates. The use of computer programs developed to solve the buckling problem of the built-up column as a two-point boundary-value problem makes it possible to establish a relationship between the modified slenderness ratio of the built-up column and the rigidity parameter of its lattices or battened plates under various combinations of boundary conditions at the ends of the column. The result of the stability analyses of the considered columns disproves the statement that the rigidity characteristics of batten plates and lacings can be ignored in determining the modified slenderness ratio for the built-up columns.

A critical live load pattern is the live load pattern that will produce the maximum axial force and/or bending moment in a structural member under consideration. Structural engineers commonly select the critical live load pattern from full-span live load patterns rather than partial-span live load patterns. In order to identify the most critical live load pattern, a three-story, two-bay steel moment frame design example is presented in this paper. In this design example, both first-order and second-order analyses are used for the determination of the required strength of the columns, while the effective length method is used for the determination of the design strength of the columns. The results of the example indicate that the effects caused by partial-span live load patterns are more critical than those caused by full-span live load patterns, not only in the computation of the required strength of the structural members, but also in the calculation of the maximum lateral displacement of the entire frame.

This paper reviews the suitability and use of post-tensioned grouted anchors to replace and/or retrofit existing Tainter gate anchorage systems. A thorough historical and theoretical review on both unbonded and bonded anchor systems was performed, a discussion is presented on the structural mechanisms by which the anchorage systems resist forces and maintain equilibrium. A review of bond mechanics is provided along with an example problem in which the two staggered anchorage patterns (Condition 1 and Condition 2) were inputted into multiple finite-element analysis (FEA) models with an assumed effective bond length and subjected to jacking load conditions. An elastic analysis was conducted for all models showcasing the peak principal stresses that developed between adjacent anchors, along with observations and comparisons between the two anchorage patterns. In addition, theoretical design concepts and example projects to retrofit existing anchorage systems are discussed along with recommendations for corrosion protection, drilling, and drilling tolerances.

The modulus of elasticity (MOE) is a key parameter in RC design. It represents the stress–strain relationship in the elastic range and is used in the prediction of deflection. Out-of-range estimations for the MOE in the existing codes of practice profoundly affected the design and performance of the concrete structures. This study included (1) the evaluation and comparison of the existing analytical models to estimate the MOE in normal strength concrete and (2) the proposal and verification of a new model. In addition, a wide range of experimental databases and empirical models, used to estimate the MOE from compressive strength and the density of concrete, were evaluated for verification of the proposed model. The results showed underestimation of the MOE for conventional concrete in the majority of the existing models. Also, considering the consistency between the density and mechanical properties of concrete, the predicted MOE values from the model, including the density effect, were more compatible with the experimental results than those from the other models presented.

In this paper, a practical calculus model based on the strut-and-tie approach for prediction of the load-carrying capacity of eccentrically loaded RC column footings with square cross sections is presented. Existing models based on beam or slab models with flexural and two-way slab punching shear failure are presented and discussed. Several subgrade contact pressure distributions for column footings are considered. A parametric analysis of the effects of footing and column dimensions (depth, width), longitudinal ratio of longitudinal steel, and strength of concrete and steel is made for all models examined. Available experimental data are utilized to verify the model in comparison with existing models. The comparison between analytical and experimental results allows one to validate the proposed model in comparison with others. Results obtained showed that by increasing the eccentricity, the load-carrying capacity decreases significantly, up to 40% for e:B = 1:6. For ratio between the compressive strength of concrete and the allowable stress on the soil between 10 and 50, the ratio B:b is between 3 and 7. Finally, simple analytical expressions are derived for a preliminary design of column footings.

Construction delays are a common problem in all the developed and developing countries costing the industry billions of dollars every year. Understanding the major delay factors for construction projects is the first step to reduce this unnecessary loss. A combined 13 studies to identify the top delay factors for construction projects in Portugal, the UK, and the US have been reported in the literature. Thirty-five construction delay factors out of a possible 42 reported in the literature have been identified as one of the top 10 construction delay factors by one of the four or five studies for each of these countries. This means that some of the top construction delay factors may not be appropriate. It is confusing to practitioners in prioritizing appropriate preventive measures to achieve better schedule performance. A thorough review of these 13 studies is undertaken to identify the top 10 delay factors for construction projects in Portugal, the UK, and the US, respectively. With respect to the construction delay factors identified, preventive measures for each major delay factor to improve the schedule performance of construction projects in Portugal, the UK, and the US are presented. The level of improvement in the schedule performance of construction projects in Portugal, the UK, and the US will depend on the extent of the implementation of the recommended measures. Similar measures can be implemented in other countries with such major construction delay factors.

Progressive collapse in structures is considered a rare event. Yet, if it occurs, it may lead to disastrous human and financial loss. A significant item to study in examining progressive collapse relates to structures with relatively large spans. In such buildings, as the adjacent column collapses, maximum damage is caused to the entire structure. Therefore, in this study, six buildings of 16 and 31 m in height were, initially, subjected to nonlinear dynamic analysis upon the removal of a column. Shell elements were employed for concrete floors, and beam elements were used for beam members, columns, braces, and truss elements for cables, taking into account the nonlinear and geometric behavior of materials. The results of the numerical models were compared with the two experimental models, and a proper match was achieved. After the analysis of the primary structures, the two strengthening methods of braces and cables were employed by the removal of the column. The results of the study indicate that the use of cables and braces is able to significantly reduce the displacement of the node over the column by using an alternative-path method. Also, these two reinforcement methods are another reason for other structural elements to remain elastic.

This article presents an experimental and analytical study related to the structural behavior of slender RC columns with normal-strength concrete (NSC) and high-strength concrete (HSC) strengthened by steel angles and battens. Twelve specimens of slender RC columns were tested, which differed in terms of the compressive strength of the concrete, reinforcement ratio, and spacing between battens. Furthermore, the axial load was applied in the experimental test with three different eccentricities (0, 20, and 40 mm). The structural behavior of the columns, such as the deflection, ultimate load, and mode of failure, was found to be significantly influenced by the strengthening. The ultimate load was increased by 50.43, 79.49, and 86.32% for the spacing between battens of 432, 288, and 192 mm, respectively, when compared with the unstrengthened column, which had 20-mm eccentricity. The ultimate load was increased by 42.86% for 192 mm, compared with the unstrengthened column, which had zero eccentricity. New analytical formulas were derived based on equilibrium equations and strain compatibility to estimate the ultimate load of slender columns with or without strengthening. The difference range in the ultimate load between the proposed formulas and experimental results of the current work and many previous researchers was 0.3–24.9%, and the average was 7.05%.

Today, concealing a longitudinal circular rainwater pipe in the center of a column cross section is common practice in the construction of skeleton RC frames. This research studies the strength reduction caused in short braced columns and the effect of factors that will increase or reduce the strength change. Sixteen columns (100 × 100 × 500 mm) were tested to investigate the effects of the hole:cross section ratio (i.e., the ratio of the hole to the cross section), concrete compressive strength, main reinforcement ratio, and ties spacing on the axial load capacity of the columns. The longitudinal and lateral deformations of the columns were measured to determine the first crack appearance and elastic work of the columns. The test results show that changing the hole diameter within the cross-sectional area has a major significant effect on load carrying capacity, in which a 5 and 1.8% reduction in the cross-sectional area caused a decrease of 20 and 10% in bearing strength capacity, respectively. However, increasing the concrete compressive strength and the reinforcement ratio does not show a considerable effect, whereas the spacing of the ties has a minor effect on the results.

For ensuring the safe load capacity of steel scaffoldings, the ultimate load capacity analysis is performed including an experimental test and numerical modeling. The test is relatively costly; therefore, it is used specifically for small configurations. Then, the parametric methods based on the calibrated numerical modeling are used. The ultimate strength analysis of steel structure requires a sophisticated nonlinear inelastic computer analysis and cumbersome procedure. As an alternative, elastic second-order computer analysis and the direct analysis method (DAM) are tried. The loading is given incrementally, and at each stage the available strengths and required strengths are evaluated. The ultimate limit load is considered achieved when the available capacity in the critical member equals that required. It has been proven that the calibrated DAM can be used to trace the ultimate load well. It can even be used to evaluate the effectiveness of bracing or lateral support placements. It is important especially for multistory steel scaffoldings that belong to sway frames because their strengths are significantly influenced by the stability issues.