Construction Imperfections Research Articles

Magnetic Shielding of Rogowski Coils

This paper describes the impact of Rogowski coil (RC) construction imperfections on measurement errors. A procedure is shown for detecting RC non-homogeneity using a rotary dipole magnetic field inducing a current inside an RC. The influence of RC magnetic shielding on reducing spurious fields is described.

Probabilistic assessment of groundwater leakage in diaphragm wall joints for deep excavations

A probabilistic method is proposed for conducting groundwater-related hazard assessments that are useful for the risk management of deep excavations in saturated soils in urban areas. The design of deep excavations, construction procedures and execution methods aimed at realizing underground infrastructure are characterized by major uncertainties related to soil properties, construction imperfections and hydrogeological site conditions. During the construction stages, geometrical imperfections and ineffective technologies to control wall seepage can strongly affect the level of risk to the adjacent built environment, leading to severe damages. The aim of this study is to provide an assessment of the leakage probability in reinforced concrete (RC) retaining walls. We model the main geo-structural factors that influence trench stability and the key geometric and technological parameters that affect construction imperfections as relevant random variables. Moreover, through Bayesian updating, useful recommendations are provided regarding the effectiveness and influence of the monitoring phase on reducing the failure probability.

Non-linear analysis of concrete structures: a practical design approach to Eurocode

Reinforced concrete is an inherently non-linear material with non-linear compressive behaviour, concrete cracking and reinforcement yielding altering the stiffness and causing redistribution of forces within statically indeterminate structures. A practical design approach is described that has been developed to ensure robust computation of serviceability limit state and ultimate limit state demand in line with Eurocode BS EN 1992, including explicit modelling of material and geometric non-linearities and construction imperfections. The approach uses the MAT_CONCRETE_EC2 material model within the LS-DYNA finite-element analysis package and has been extensively used during the detailed engineering design of the concrete gravity substructure for the White Rose Extension Project off the coast of Newfoundland, Canada. The material model and validation of its behaviour in accordance with the Eurocode standard are described, along with other typical engineering applications where the approach may be of benefit. Specific benefits and implementation challenges encountered during the design process are also highlighted with a non-linear buckling assessment case study.

The Impact of Using Concrete of Various Density on the State of Stresses in Prestressed Concrete Flyovers Over Highways

A significant part of flyovers over highways and express roads in Poland is developed as two-span beam and frame structures. Due to the span length and economic conditions their superstructure are most often constructed as prestressed concrete ones. This paper presents the impact of some of the construction defects and imperfections not considered during the design stage on the stress state in the post-tensioned flyovers structures over highways. The results of the analyses concern three structures that were inspected in detail by the authors.

Effects of the Equivalent Geometric Nodal Imperfections on the stability of single layer grid shells

The present paper discusses the sensitivity of the global and local stability of a hybrid single layer grid shell to a set of Equivalent Geometric Nodal Imperfections representative of the actual structural and construction imperfections. Since imperfections are hard to be measured and controlled in experimental facilities, the stability of the structure is extensively investigated in numerical experiments. The imperfections are set by means of the so-called Eigenmode Imperfection Method. The method parameter space is densely sampled, and different structural models are adopted. The results are given in terms of two bulk parameters: the well established Load Factor and the proposed Buckling Shape Length, the latter being introduced to provide a continuous measure of the degree of “globalness” of the instability. Significant and non monotonic changes in both the Load Factor and Buckling Shape Length are observed versus the growth of the imperfection amplitude. Further, a local metrics of the grid shell geometry, named nodal apex, is introduced for each structural node. Special emphasis is given to the analysis of the correlation between the apex of the initial imperfect geometry and the apex of the deformed shape at collapse. The observed high correlation suggests that the mechanical behavior of the imperfect grid shell is significantly influenced by this local geometrical feature.

Behavior of pile group incorporating dissimilar pile embedded into sand

Piles are recommended to transfer the superstructure loads safely through soil by friction resistance and end bearing into firm bearing stratum. Piles drive their load via weak soil into competent bearing stratum. Piles in group are designed of similar length, diameter and working load. Except in special cases such as raft on piles which may be attentionally of different lengths. Dissimilarity in piles within a group may result from uncertainties in soil conditions, or imperfection in pile construction. Soil conditions may force the designer to design pile groups in a building having different lengths. Studying the behavior of pile groups incorporating dissimilar piles, in literature is scarce. The paper is devoted to study, through small scale models in laboratory, the behavior of pile groups incorporating one dissimilar pile. The aim of the research work was to emphasize the effect of dissimilar pile on the behavior of pile group through load settlement relationship. The study revealed that the end bearing of the group due to the existence of dissimilar pile, decreases as the number of piles in the group increased. The deficiency of two-pile group containing one dissimilar pile attains 90%, while in a group containing 9-piles it reaches 5%.

Risk and damages assessment of industrial objects by structural and logic decomposition of enterprises

It is shown the sequence of application of systems engineering in the analysis of possible accidents in industrial plants, when a failure in one of the subsystems can serve as a trigger to the emergence and development of the accident in the other subsystem. System analysis and modeling of basic processes in the technosphere are particularly relevant at the moment, when a high degree of deterioration of power and technological equipment lead to accidents with consequences that difficult to predict. The current crisis situation in matters of accident and injury due not only to poor safety culture and technological personnel indiscipline, but constructive imperfections and more deterioration of industrial equipment. Research of risk and safety are affected, primarily due to lack of a unified and coordinated methodology. Using different methods and criteria leads to sub-optimal decision-making, economic costs and imminent risk of major accidents. As the basic scientific method with further study the risks and damages in industrial enterprises (IE) are used the systems engineering and energy and entropy concept that considers the incident as an unwanted release of energy or harmful substances that accumulate in technological objects. In this case, the IE as the man-machine-environment system is man-made damage as a result of an accidental release, transformation, distribution and devastating impact on the resources of IE (including and human).

Comparison of bolted end plate and T-stub connections sensitivity to bolt diameter on cyclic behavior

Considering the construction limitations, proper and correct design of connections is vital and of great importance. At the construction stage, it is probable to use a connection bolt with a diameter less than the design assumptions. It can occur due to an imperfection in construction or even to changes in the function of the building. The unforeseen changes can increase the structural load, and consequently the moment and shear force demand values. Therefore, the present paper is aimed to examine the sensitivity of the bolted connections to the diameter of bolts using a numerical method. The results show that bolted T-stub connections are more sensitive to bolt diameter than end plate connections. Hence, the bolted end plate connections are recommended where the imperfection in construction or changes in function of the building is probable. Moreover, in construction of bolted connections, if changing the number of bolts regarding the constant total cross sectional area is considered, it is recommended to use the symmetric arrangement of bolts on each beam flange. In design of connections for a particular frame according to AISC, the moment capacity of T-stub connection is higher than that of end plate connection. However, the total energy absorptions of these connection types are approximately equal.

Comparison of bolted end plate and T-stub connection sensitivity to component thickness

A connection shall be designed so that inelastic behavior is controlled either by flexural yielding of the beam in combination with shear yielding of the column panel zone, or by flexural yielding of the beam alone. At the construction stage, it is probable to use a connection component with a thickness less than the design assumptions. It can occur due to an imperfection in construction or even to changes in the function of the building. The unforeseen changes can increase the structural load, and consequently the moment and shear force demand values. Therefore, the as-built thickness of the connection component would be less than the required amount. The present paper is aimed to compare the sensitivity of the bolted connections to the thickness of the end plate and T-stub flange using a numerical method. The results show that the bolted T-stub connections are more sensitive to component thickness rather than end plate connections. Hence, the bolted end plate connections are recommended where the imperfection in construction or changes in function of the building is probable. Moreover, in the design of connections for the same frame according to AISC, the moment capacity of a T-stub connection is higher than that of an end plate connection. Furthermore, the moment capacity of the stiffened end plate with a thinner end plate is higher than that of an unstiffened end plate. Because of the better hysteretic performance of the stiffened bolted end plate connections compared to the unstiffened bolted end plate connections, the application of the former is recommended.

Characterization of Deformed Magnets From External Magnetic Measurements

Due to the unavoidable construction tolerances and imperfections in the assembly of coils, the actual magnetic field of manufactured magnets differs from the design one. Depending on the consistency and the profile of the field error, a number of problems may arise, especially in high-performance devices, such as magnets for nuclear magnetic resonance or thermonuclear fusion devices. Typical quality insurance procedures can hardly reveal possible winding pack (WP) deformations. In this paper, deformed magnets are characterized by means of a limited set of parameters, providing an equivalent magnetic behavior, and an assessment of limits and possibilities of such a WP characterization from external magnetic field measurement is discussed, including some aspects of the inverse problem resolution.

Influence of executive imperfections of railway steel bridges construction on operational capacity and fatigue capacity

In recent years, in our country are modernized and rebuilt several sections of railway lines, mainly main lines. The greater part is adapted to increased speeds. However, such an adaptation involve the reconstruction or construction of new bridges including steel ones. The paper concerns the executive imperfections of constructions of steel bridges which in recent years have been built in the modernized main railway lines. These imperfections consist of, among others, the geometric imperfections from the assumed construction project. This also applies to defects in welds of various types that occur in critical elements of bridge structure. The aim of this paper is to demonstrate the influence of imperfections on the load carrying capacity and fatigue of these structures. Author showed that the observed imperfections have a significant impact on the fatigue life - especially for weld defects, in the case of load carrying capacity their importance is much smaller. These analyses are performed by using the theoretical methods developed in previous reports. In the analysis new standards for the design of steel structures from Eurocodes group were used.

Diagnostics of Drum Type Wood Chipping Machines

This paper investigates diagnostic methods and proposes modern service technologies for wood-processing equipment. The aim of this study is to ensure systematic, research-based wood-processing services and continuous, no-failure operation of facilities. We describe the working principle of a particular industrial, drum-type wood chipper and discuss the problems that occurred during operation, including potential excess engine load or construction imperfections. First experiments show that knife wear progresses even faster than previously expected. Cutting regime calculations are provided, along with a description of actual improvements and a comparison of cutting regimes before and after improvements. The intended result of this research is a monitoring unit with help of a few modifications, can be used on any drum-type wood processing equipment.

Continuously Reinforced Concrete Pavement

In 2005, the Texas Department of Transportation initiated a rigid pavement database to collect information in preparation for the calibration and potential implementation of the Mechanistic–Empirical Pavement Design Guide (MEPDG) for continuously reinforced concrete pavement (CRCP). Twenty-seven sections, each 300 m (1,000 ft) long, were selected throughout the state. Deflection testing was conducted with a falling weight deflectometer. The information collected included load transfer efficiency (LTE) at small, medium, and large crack spacing for two different seasons, summer and winter. Also collected were crack-spacing information and slab deflections. LTE values for all the cracks were higher than 90% regardless of slab thickness, pavement age, crack spacing, or season. Mechanisms of primary distresses in CRCP were investigated. The investigation tentatively revealed that many distresses identified and recorded as punch-outs in Texas were not actually caused by structural deficiency. Rather, most of the distresses were caused by imperfections in design details, construction or material quality issues, or both. Horizontal cracking appears to be the major cause of distresses in CRCP in Texas. The interactions between longitudinal steel and concrete in response to dynamic wheel loading applications appear to be the cause of horizontal cracking. From the findings, mechanistic–empirical (ME) CRCP design procedures and a calibration function were developed. Because the accuracy of any ME design procedure depends to a great extent on the reasonableness of the transfer function, further efforts will be made to improve that function.

Cyclic behavior of bolted connections with different arrangement of bolts

During the 1994 Northridge earthquake, relatively poor performance of the bolted web-welded flange connections (BWWFs) was observed. Thereafter, various types of connections such as end plate and T-stub bolted connections were suggested to be used in moment resisting frames that are often used in industrial and tall buildings. In this paper, finite element simulation is used to study and compare the cyclic behavior of fourteen specimens of the mentioned connection type by changing the horizontal and vertical arrangement of bolts. The results show that the moment capacity and the initial rotational stiffness of T-stub bolted connections are higher than that of end plate bolted connections designed based on AISC considering the total energy dissipation of both groups to be approximately equal. It is also evident that the probability of failure mode change in T-stub connections is higher than that of end plate connections under cyclic loading due to the arrangement variation of bolts. Based on the results of this paper, end plate connections are suggested for conditions where the imperfection in construction is probable.

Acoustic emission activities and damage evaluation of reinforced concrete beams strengthened with CFRP sheets

In this study, the applicability of acoustic emission (AE) techniques to monitor damage evolution in reinforced concrete (RC) beams strengthened in flexure with carbon fiber reinforced polymer (CFRP) sheets is investigated. The objective is to initiate the creation of a user-friendly health monitoring system for RC structures strengthened with CFRP sheets using AE techniques. Five beams, 200mm×300mm in cross-section, were tested under three-point bending over a span of 1700mm. One of the beams was tested in its virgin condition to serve as reference; the remaining four beams were tested after being strengthened with CFRP sheets bonded on the tension face. The parameters investigated in this study include both the amount of CFRP sheets and construction imperfections (the CFRP sheets were intentionally bonded without adhesive in the centermost 10% and 20% bonding area). The AE signals were collected and analyzed for all specimens. The AE parameters were analyzed for four levels of damage based on initial crack, propagation, yielding of main bars, and fracture or rip-off of the CFRP sheets. The frequency-peak magnitude distribution of the AE parameters was used to determine the b-value, defined by the Gutenberg–Richter relationship, for evaluating the damage evolution and fracture process of RC beams strengthened in flexure with CFRP sheets. From the results of this study, the signal characteristics – event, amplitude versus frequency, and amplitude versus duration – show clear differences in the different loading stages, depending upon the active damage mechanism. The b-value is correlated to the fracture process of the RC beams bonded with CFRP sheets and the degree of localization of damage. The AE technique is a useful nondestructive technique for monitoring the behavior of RC beams that are externally reinforced in flexure with CFRP sheets.

Performance of the PR connections under combined Axial-tension and moment loading

The inherent moment capacity of bolted top-seat angle connections with double web angles (TSDW), categorized as partially restrained (PR) connections according to AISC-LRFD specifications, can be considered in analyses of semi-rigid connections especially when an accurate analysis of such fames is desired. However, in some cases, developed internal forces in the frame elements may affect the connection behavior, considerably. Axial tension force is one of such internal forces that may be imposed on frame connections in some cases such as construction imperfections, seismic loading or under large deflections of the catenary action during the progressive collapse of the semi-rigid frames. This study aims at the effects of the axial tension force on the performance of the bolted TSDW angle connections using nonlinear finite element method (FEM). The obtained results show that the axial tension force reduces the connection moment capacity and stiffness, considerably. Based on the obtained moment-rotation curves, affected by this particular loading type, equations are proposed to estimate the reduction rate of the connection stiffness and moment capacity.

TESTING THE PRINCIPLE OF EQUIVALENCE IN AN EINSTEIN ELEVATOR

Improving the level of accuracy in testing the principle of equivalence (PE) requires reliably extracting a very small signal from an instrument's intrinsic noise and the noise associated with the instrument's motion. In fact, the spin velocity required to modulate a PE-violating signal produces a relatively high level of motion-related noise and modulation of gravity gradients at various frequencies. In the test of the PE in an Einstein elevator under development by our team, the differential acceleration detector free-falls while spinning around a horizontal axis inside an evacuated, comoving capsule released from a stratospheric balloon. The accuracy goal of the experiment is to test the PE at an accuracy of a few parts in 1015, a limit set by the expected white-noise sources in our detector. The extraction of a very small signal from the prevailing noise sources is necessary for the experiment to succeed. In this paper, we discuss different detector configurations and describe a particular design that is able to provide a remarkable attenuation and frequency separation of the effects of motion and gravity gradients with respect to a PE-violating signal. Numerical simulations of the detector's dynamics in the presence of relevant perturbations, realistic errors, and construction imperfections show the merits of this configuration for the differential acceleration detector.

ION SOURCE FOR MONOPOLE MASS SPECTROMETER

The results of simulation of an industry monopole mass-spectrometer ion source with SIMION 3D software are described. Construction imperfections are disclosed. The results of the analysis are checked experimentally by the ion source modifica­tion for a МХ7304АМ monopole mass-spectrometer. A new construction of the ion grid source is proposed with better characteristics and operating parameters.

Discussion of “Pile Behavior—Consequences of Geological and Construction Imperfections” by Harry G. Poulos

The author must be commended for giving another remarkable contribution to foundation engineering. Designs are almost always made assuming ideal situations, but geological and construction imperfections do exist. Especially in the case of bored piles, one must recognize that construction effects have a major influence on their stiffness. A very competent designer, using very reliable soil information and an extraordinarily precise method for predicting the bearing capacity of a pile, may, in some cases, make a not-so-reliable prediction. In other words, these very favorable conditions alone do not guarantee a successful design. The reason is that in the design phase no one knows how the pile is going to be built. The author has shown very clearly the influence of a “soft base” in the stiffness of a pile. Fig. 25 shows that for a given load, the pile with “unclean” base settles about three times more than a similar pile with a “clean” base. And it is not a 20 or 30% difference, but a 200% difference. The discusser would like to add new information on this matter. The case of a foundation for a large industrial plant will be analyzed. The foundation consisted of about 4,000 mechanically drilled bored piles, 70 cm in diameter. The soil was a compacted fill. The design specification required that after finishing the drilling procedure, the walls of the shaft should have to be cleaned by a foreman using steel brittle brushes. After that, the bases had to be cleaned and then, the pile concreted. To evaluate the influence of the “cleaning” procedure on the bearing capacity of the pile, two load tests were carried out. Although the two test piles were close to each other and within the same compacted layer, it was decided to carry out two SPTTs. The SPT-T is the traditional SPT complemented with torque measurements, Decourt and Quaresma Filho 1994 . In order to reduce the influence of soil heterogeneity on the results, the discusser required the axes of the piles to coincide exactly with the axes of the borings SPT-T . The results of the two SPT-Ts were very close to each other, so it was considered that direct comparison between the two load

Closure to “Pile Behavior—Consequences of Geological and Construction Imperfections” by Harry G. Poulos

Closure to “Pile Behavior—Consequences of Geological and Construction Imperfections” by Harry G. Poulos