Column Heads Research Articles

Analysis of deformations of road embankments founded on displacement columns improving soft subsoil

Drilled displacement columns, constructed in the form of unreinforced or reinforced concrete elements, are currently a very commonly used method of improving soft subsoil, creating an alternative to more expensive pile foundations. A frequently used solution for improving soft soils of road or railway embankments is to design a regular pattern of columns of relatively small diameter. Columns along the perimeter of the improved area are reinforced with rigid steel profiles, while the internal ones are made as concrete elements. Column heads are usually covered with a load transfer platform (layer of compacted granular fill) which is additionally reinforced with geosynthetics. The application of soil improvement with displacement columns is not always successful. It is due to the errors and shortcomings occurring at the design stage, including simplifications in modelling, to construction faults, which may include insufficient experience of contractors and/or improper supervision. Referring to the real object that failed, the article provides the results of numerical parametric analyses taking into account the influence of the key design parameters such as: the stiffness of the load transfer layers, the amount and stiffness of the geosynthetic reinforcement as well as the column spacing. The article presents comparisons of numerical results obtained with the finite element analyses for various approaches to geometry modelling (axisymmetric, 2D and 3D). The simulations indicate that the use of the axisymmetric model of a single column in routine design may lead to the deformations exceeding the serviceability limit states.

Evaluating stability of rigid-column-supported and geosynthetic-reinforced embankments

Field observations and centrifuge tests indicate that progressive column bending failure accompanies most instabilities of rigid-column-supported and geosynthetic-reinforced (RCGR) embankments. However, recognized guidelines specifically for evaluating the overall stability of such systems featuring bending failure remain limited. A general methodology to calculate the factor of safety (FS) for RCGR embankments using the limit equilibrium method is presented in this article. The focus is on deep-seated slope failures, wherein rigid columns progressively fracture due to subsoil overstressing. The concentric arches model, along with tensioned geosynthetic analysis, informs the determination of vertical and horizontal loads on the column heads. The column's resisting moment stems from its flexural and compression resistance. A mobilization factor for the net thrust on each column is defined to capture the progressive failure. The methodology involves an iterative computational procedure to identify the critical slip surface and the FS using the Fellenius' method. The solution was validated using three case studies, including both centrifuge models and field tests, as well as finite-element analysis. The results indicate that the soil mass contributes the most to resisting sliding and overall stability, followed by columns and geosynthetics. In addition, axial force mainly provides the resisting moment of columns.

Geosynthetic-encased columns (GEC): A proven case study over 30 years

The construction of embankments on very soft soils is a challenge due to the low shear strength, low permeability, high compressibility, and high-water content of the subsoil. The surcharge load imposed by the embankment can result not only in a local or total loss of stability but also in unacceptable settlements and horizontal deformations or thrusts, which could endanger nearby structures. To overcome these problems, different construction methods are applicable. One particularly interesting and still innovative foundation system is the use of geotextile encased granular columns, which can be considered “State-of-the-Art” in Europe. It was developed and introduced in 1994, and since then many major projects have been realised using geotextile encased columns (GEC). The overall loads and stress concentrations above the column heads induce outwardly directed radial horizontal stresses in the columns. The particularity of the GEC system is that these stresses are counteracted not only by the inwardly acting pressure of the soft soil but also –most importantly – by the radial resistance of the tensile stiff geotextile casing. This paper briefly describes the GEC system and includes the description of a few notable projects using GEC as a foundation system: land reclamation at the Airbus site in Hamburg, Germany, and the Second Niger Bridge in Africa. The geotechnical challenges, design basis, and what can be considered the most important findings of each of these projects are also discussed in this paper.

CALCULATION OF WELLHEAD PARTS

Wellhead rigidly connects the entire working column into a single system, takes the load arising from their weight, and transfers the entire load to the conductor. Provides insulation and tightness of the space between the columns, while at the same time allowing you to monitor the condition of the wellbore and perform the necessary technological operations. Wellhead serves as a pedestal for installing the production string lowered into the well. During drilling, blowout preventer equipment is installed on it, which is dismantled after drilling. The number of these elements depends on the number of working strings in the well. The casing head is positioned according to the sequence of running and cementing at the wellhead. They are selected during drilling taking into account the expected formation pressure after the drilled well interval. The operating conditions of the column head are quite difficult: In deep wells, the load from the weight of protective casings can exceed several hundred kilonewtons. The column head elements also absorb the pressure of the medium in contact with them. If there is H2S, CO2 in the formation fluid or gas, or if the formation water is highly mineralized, the casing is subject to corrosion. When the heating agent is injected in deep wells, their tubing head and casing head heat up to 150-250° C, and in the Northern conditions it cools down to -60° C. Violation of the reliability of the column head leads to serious accidents, and in some cases – fires and explosions In particular, the casing heads of multi-casing wells have a large mass and vertical size. Their high metal intensity and high demand require the expenditure of large amounts of steel, especially alloy steel, for their production. As the vertical size of the casing head increases, well maintenance becomes more complicated. Column heads for wellhead equipment are manufactured with different numbers of protective columns: three-, four- and five-post. The principle and design diagrams of such column heads are similar. Keywords: wellhead, casing hanger, equivalent tension, cylindrical part, flange.

Compression behavior of RC wall-like columns strengthened using NSM/CFRP system without shape modification

The wall-like columns are commonly employed in high-rise buildings for carrying heavy loads without affecting the usable space. However, the retrofitting of these columns often becomes essential under some circumstances. Thus, the designers are looking for strengthening schemes that do not cause changes in the column section for which a combination of near-surface mounted (NSM) bars and carbon fiber reinforced polymer (CFRP) confinement can be adopted. This study was undertaken with the objective of developing such a scheme and studying the confinement provided by CFRP wrapping on wall-like columns. In this study, besides testing two control columns, four columns strengthened using different schemes were tested in axial compression. The performance of the schemes was assessed in terms of the failure modes, load-carrying capacity, and different characteristics of the load-displacement plots. The best scheme was found to be the one wherein the column was strengthened using NSM steel bars connected to the column heads, along with the wrapping of three CFRP sheets covering the NSM rebars. Two analytical models were proposed to estimate the peak load. The first model used the approach of both the ACI 318-19 code and ACI 440.2R-17 guidelines, whereas, the second model utilized the formulas of both Eurocode 2 and the ACI 440.2R-17. The second model predicted the peak load of retrofitted columns more accurately than the first one with prediction errors for the second model varying from 2% to 9%.

An analytical and numerical study on influence of the load transfer shallow mixing layer on stress-induced and settlement of ground improved by CDM columns

In the literature, there are a few analytical methods for evaluating stress induced on the CDM column heads and most of them involve the use of geosynthetics embedded layers, except the method of ALiCC. However, the ALiCC method still has some limitations in actual designs. This paper presents numerical analysis (by using Plaxis software) and analytical analysis (by using the ALiCC method) on the influence of thickness and stiffness of the SM layer (without the use of geosynthetics embedded layers) on stress induced on column heads and settlement of the improved ground. A typical parametric case and actual project case were taken into analyses. Analysis results from the examined cases indicate that, as expected, when the thickness or stiffness of the SM layer increases, the settlement of the ground decreases and the stress induced on the column head increases. An important finding from this study is that the maximum stress induced in the CDM column is typically not on the head of the columns but at the middle depths where soil layers are softer than the SM layer and the bearing layer at the column toes.

Traces of Islamic Architecture in the Design of the 'Gedung Sate' in Bandung

Gedung Sate was built to accommodate various architectural styles derived from local and foreign elements. The local elements have been widely studied, such as those relating to the architecture of the 'Candi' on the island of Java. Many external elements are associated with the Moorish European style and that of the Dutch. However, according to the elements, it also indicates the existence of Indian Islamic architecture, the Mughal style. This study of the Islamic elements of Mughal India has not been pursued or presented any further. This study aims to identify the traces of Islamic architecture in the Gedung Sate, especially those derived from the Mughal, Moorish and local styles. This research method used a qualitative approach by studying the morphology of Gedung Sate and Mughal or Moorish buildings to identify the relationship between their architectural elements. The results show that Gedung Sate does indeed show the use of Mughal architectural elements, especially in the outer layout and mass, processing of the figure section, and the ornamental exterior column, while the Moorish influence is more visible in the processing of curved elements and column heads and slender interior columns showing light elements. The idea of using Islamic architecture is carried out to represent the splendor in the typology of new buildings in the prospective capital city of the Netherlands Indies, namely Bandung. Indian architecture is used as a reference because it is considered to have a close relationship with Candi as an important resource in Java.

Design & Analysis of G + 5 Residential Building with Comparison of Conventional Slab and Flat Slab using ETABS

Abstract: In the conventional method, a beam with a large beam depth and a small slab thickness supports the slab. The weight is transferred from beams to columns. The flat slab is method in which the slab is resting directly on columns .The flat slab allows architects to provide partition wall wherever it is needed. To supports heavy loads and thickness of slab near the support with the column is increased and these are called drops ,or columns are provided with enlarged heads are called column heads .As the beam is not there in flat slab it gives the plain ceiling consequently giving better architectural appearance. The flat slab building is used these days because these structures offers many benefits which a normal slab structure does not provide .The objectives of this project is to compare multi-storey residential building having flat slab with conventional slab . The design and analysis is done by using ETABS software. This present work provides reasonable information about the stability of flat slab.

Analisis Riwayat Waktu Nonlinier Struktur Flat Slab dengan OpenSees Navigator

Structural systems that do not use a beam as the main component were first developed by Turner in 1906. This structural system is better known as a flat slab. The flat slab structure is supported by column heads and drop panels, or without drop panels, or without column heads. Several building codes such as IS 456: 2000, ACI 318-08, ACI 318-19, EC 2:2004, and NZS 3101 (Part 1):2006 provide guidance for designing flat slab systems under gravity loads only. However, many flat slab buildings are also built in areas with high earthquakes which can cause the collapse of buildings due to earthquake loads. In this paper the 10-level flat slab building structure design results are analyzed using nonlinear time history response analysis with the help of OpenSees Navigator software using several earthquake records, namely Kobe (Japan, 1995), Imperial Valley (California, 1979) and Tabas (Iran, 1978) which has been adjusted to the design spectra of the city of Yogyakarta. From the results of the analysis using OpenSees Navigator, it was found that the story drift that occurred was still within the limits required in the regulations, so that the building being reviewed was still within the limits of life safety design.

Modelling using finite element analysis in the structural behavior of bubble deck slab

Bubble deck slab is the one which is set up by placing voids in the form of bubble which decreases dead weight and is an ecologically friendly practice. In this technique any part of concrete which is not performing any building function will be eliminated. Therefore, helps to reduce the dead weight in the structure. In this insufficient concrete is replaced by the bulk polyethylene round sphere. The benefits are material savage, quick construction time, decrease weight, less liberation of waste gases also a green technology too. In this, it has designed a voided bubble deck slab. The procedure for eliminating concrete in a conventional slab is by incorporating the bubbles in the slab by reducing dead weight of the slab in which there is no structural performance and by increasing proficiency of the slab. This technology is mainly to minimize the volume of concrete by replacement of concrete by the plastic sphere, that is available locally. This technology does not require column and beam heads and that can be used in ground floor slabs and roofs. This technology is more economical and reduces the cost in construction. Here, Comparative analysis between traditional slab and bubble deck slab using Abaqus software.

A highly sensitive gas chromatograph for in situ and operando experiments on catalytic reactions.

We describe an automated gas sampling and injection unit for a gas chromatograph (GC). It has specially been designed for low concentrations of products formed in catalytic in situ and operando experiments when slow reactions on single crystal models are investigated. The unit makes use of a buffer volume that is filled with gas samples from the reactor at a reduced pressure. The gas samples are then compressed by He to the injection pressure of 1000mbar and pushed into two sample loops of the GC, without major intermixing with He. With an additional cryo trap at one of the GC column heads, the designaims at concentrating the gas samples and focusing the peaks. The performance is characterized by experiments on the Fischer-Tropsch synthesis, using H2/CO mixtures (syngas) at 200 and 950mbar and a Co(0001) single crystal sample as model catalyst. Chromatograms recorded during the reaction display sharp, well separated peaks of saturated and unsaturated C1 to C4 hydrocarbons formed by the reaction, whereas the syngas matrix only gives moderate signals that can be well separated from the product peaks. Detection and quantification limits of 0.4 and 1.3 ppb, respectively, have been achieved and turnover numbers as low as 10-5s-1 could be measured. The system can be combined with all known analysis techniques used in in situ and operando experiments.

A case study of a dcm column-supported embankment over soft clay

ABSTRACT This paper investigates a case study of a highway embankment in Thailand constructed over Deep Cement Mixed (DCM) column improved ground. The case study was simulated using a 2D plane-strain model adopting the equivalent area approach for columns. Field measurements for deformations and excess pore pressures are compared with the finite element results to verify the numerical model, and to understand the load transfer mechanism. The most likely failure mode of the embankment was investigated by computing the Factors of Safety (FOS) against the bearing failure and bending failure of individual DCM columns, and the overall stability of the embankment. Results show that the most likely failure mode for this embankment is the bending failure of attached columns underneath side slopes. In the case study, attached columns are used to control the lateral deformations. In the paper, three other approaches used in practice for lateral deformation control are investigated: (i) Load transfer platform (LTP) with a geosynthetic layer above DCM columns with single columns near the side slopes (ii) T-shaped single columns near the side slopes and (iii) Reinforced single columns near the side slopes. Results show that in this particular case, due to the presence of a relatively deep fill layer above the soft clay deposit, lateral deformation control measures applied closer to the column heads such as LTP or T-shaped columns are not effective. However, the use of double columns with increased bending stiffness throughout the soft clay layer or increasing the length of columns underneath the embankment is the most effective solution in reducing lateral deformations.

New insights into soil arching behaviour in column-supported embankments

The observation of failure surfaces within column-supported embankments is critical to understanding how the embankment stresses are transferred towards the column heads. In this study, finite element simulations utilising a strain-softening constitutive model, nonlocal regularisation, and the Arbitrary Lagrangian–Eulerian formulation are used to examine these failure surfaces over various embankment geometries. This methodology offers insights into the nature of the failure mechanism, the development of a plane of equal settlement, and the influence of the subsoil settlement profile. Depending on the embankment geometry, the results indicate a punching failure, inverted general bearing failure, or a localised failure develops. The transition between punching and inverted general bearing failure is found to be closely related to the establishment of a plane of equal settlement within the embankment. The height of the plane of equal settlement and the range of failure mechanisms that develop were largely insensitive to the nature of the subsoil settlement profiles simulated. These findings have implications for the practical design of efficient embankments and the effective design of future experimental studies.

Numerical simulation of the progressive development of soil arching in column-supported embankments

The soil arching mechanism is partly responsible for the transfer of stresses away from the soft subsoil and towards the relatively stiff column heads in column-supported embankments. Experimental studies have shown that the load transfer resulting from soil arching evolves progressively with increasing subsoil settlement. Past numerical studies exploring soil arching in column-supported embankments have typically not been able to capture this progressive development of load transfer. A series of improvements on past numerical studies are outlined that allow for improved simulation of the soil arching mechanism in column-supported embankments. These improvements include implementation of a strain-softening constitutive model, non-local integral type regularization and the application of the arbitrary Lagrangian–Eulerian finite element method. The benefits of these improvements are observed through comparison of simulation results to recent experimental studies of column-supported embankments. The comparison indicates that these techniques allow key aspects of soil arching kinematics and mechanics to be captured.

Review of Punching Shear Strengthening Methods [Case Study: Application of Post Installed Shear Bolt Papers

Flats slabs became a common solution for buildings because they are easy and fast to build. In the last few years, some building that constructed using flat slab system required strengthening for column to slab junction due to either some imperfections during design, construction or due to increase of the design load in case of change of the building function. The common strengthen methods against punching shear (column heads, drop panels) leave an obvious trace which in most cases conflicts with some extensions parts and may reduce the height of the story considered, thus it can’t be applied in such cases. A relatively new technique was studied, it consists of high tensile steel bolts installed vertically through the slabs by drilling and bonding with high-performance epoxy adhesive and mechanically anchored to the slab surface. Many studies validated the efficiency of the technique in strengthen against punching shear and also in enhancing the ductility of the slab-column connection and the results shows that the method can be applied in practice. In this paper, the post-installed bolts technique is presented and applied in a practical case study. The capacity of the slab enhanced by 53% and it was easy to design and construct. Also, it took not more than few hours for its application. In addition, the building extension utilities (Heating ventilation and air conditioning, communications...etc.) was not harmed because the slab surface remains clear. Those advantages make the technique a favorable option for owners and engineers when strengthening against punching shear.

3D simulations of deep mixed columns under road embankment

When column stabilisation is meant to function as a ground improvement under an embankment, the design cases to be considered consist of overall stability, compression resistance of the column heads, arching of the embankment on the columns and settlements. This paper focuses on the compression resistance of the columns. The proper geotechnical design of deep mixed (deep stabilised) columns under road embankment requires good estimation of the stress-strain behaviour of the columns and the surrounding soil under the embankment and traffic loading. Earlier Finnish design approaches relied on an even traffic load of 10 kN/m2 on the road surface. The dimensioning methods for column stabilised soil are also based on the idea of an even traffic load. Due to Eurocode recommendations a more realistic scenario is introduced, which remarkably increases the magnitude of the traffic loading. After deriving suitable material properties and stiffness parameters for static and dynamic traffic loading, three-dimensional finite element calculations are performed to achieve better understanding of the mechanical interaction between the embankment, columns and soil under the new loading configuration. Even though more investigations are needed before delivering a final statement, the calculations show that, for the considered case in this paper, the new loading scenario has no relevant consequences on the design compared to the earlier design approach.

Roles of timber tie-rods to reduce seismic vulnerability of historical buildings in Egypt

Historical un-reinforced masonry (URM) buildings in Egypt from the medieval period generally comprise timber tie-rods that link the arches of arcades at the top of the column heads and along the arcade plane (in-plane). Usually, additional tie-rods are found perpendicular to the arcades (out-of-plane). Timber ties can also be used between facing tall URM bearing walls to minimise their buckling vulnerability. They play a considerable role in resisting seismic forces and minimising the deficiencies of URM buildings. A limited experimental investigation and a wide analytical campaign were conducted on two model buildings with the prevailing dimensions and materials of historical medieval buildings in Cairo by employing finite-element three-dimensional modelling. The focus of the work was the roles timber tie-rods play in the seismic stability of parallel-arcaded and cross-arcaded URM historical buildings. A proposal for enhancement of the seismic resistance of parallel-arcaded systems using a steel bracing system is provided.

Design of geosynthetic reinforced column supported embankments using an interaction diagram

Geosynthetic reinforced column supported embankments predominantly utilise two mechanisms to transfer embankment loads towards column heads, soil arching and membrane actions. When undertaking the design of column supported embankments, it is common practice to perform a two-step design, whereby the arching actions are estimated independently of the subsoil deformation and membrane actions. This approach is unable to capture the deformation dependency exhibited by both arching and membrane actions. This paper presents deformation dependent arching and membrane action models and implements them within an interaction diagram. It is shown that an interaction diagram-based design approach is capable of performing an ultimate and serviceability limit state design of a geosynthetic reinforced column supported embankment. In contrast, most existing analytical design methods only consider the ultimate limit state. The proposed method is applied to a design example where the benefits of such a design approach are demonstrated.

Loads acting on the equipment’s destructive elements for removing the reinforced concrete piles’ ends

Cutting off the reinforced concrete piles’ column heads is an important technological operation in the pile foundation construction. High-quality reinforced concrete piles column heads cutting should be performed at a given mark, without cracking concrete below the cut level. At the same time, reinforcing rods of the pile together with concrete are not removed. The rational equipment design for cutting the reinforced concrete piles’ column heads is complicated by the lack of information on the required forces developing on the working body of the machine. The theoretical justification of these forces is not possible, due to the lack of appropriate guidelines. To this end, the article presents the experimental studies’ results to determine the loads on cutting elements when cutting a reinforced concrete pile of square cross section. The experimental work technique is described, the conclusions of the study are presented.

Analysis of the causes of casing head in the oil and gas complex of Ukraine

The casing head is the main wellhead equipment of gas and oil wells. Column heads are installed on all wells, regardless of how they are operated. Anti-blowout equipment is installed on column heads during drilling, and fountain fittings are installed during well operation. They hang all the casing pipes lowered into the well. The design of the pillar trim provides the ability to: restore the integrity of annular space, flow in the packer space grease lubricant; crimping flange connections; monitoring and exploration of the medium pressure in the annular space; well cementing process. Violation of the column head reliability inevitably leads to serious accidents, damage to the environment, and in some cases may cause fires, explosions, accidents. The article classifies column bindings that are used in the oil and gas complex of Ukraine, according to the design of nodes for sealing inter-column heads. The causes of column head leaks of all groups are determined. The conditions of column head sealing are described. The causes of rubber aging are determined. The effect of casing string parameters on the casing head tightness is shown. Regulatory documents, describing the procedure and rules for selection, installation and oper-ation of column heads at operational oil and gas wells and wells in underground gas storage are analyzed. The analysis of modern casing heads showed that the main sealing elements of the annular space are rubber parts made of rubber. Measures to improve the column head reliability are proposed.