Journal of Structural Engineering

Comparison of sectional and strut-and-tie methods for design of pile caps

Indu Geevar, Aysha Zeneeb Majeed, Bijily Balakrishnan — Wed, 05 Jun 2024 00:00:00 +0000

Pile caps are deep members provided under the column to safely transmit the loads to the piles beneath. These members can be classified as disturbed regions, due to their low shear span-to-depth (a/d) ratios and traditional sectional methods of design are not valid. These members are popularly designed using the strut-and-tie method. The Indian standards do not have recommendations for strut-and-tie based design and designers usually adopt the sectional method of design considering flexure, shear (one-way and punching), and bearing strengths. The study attempts to compare the strength estimation of pile caps using sectional method in IS 456 and the strut-and-tie method as in ACI 318. The strut-and- tie method predicted about 1.8 times more strength than sectional method for pile caps with shear span-to-depth (a/d) ratios less than 0.9. For a/d > 1.0, the difference in strength prediction is not very significant. Previous studies have shown that the sectional method can lead to unsafe design. Hence, the study strongly recommends strut-and-tie method of design especially for deep pile caps with a/d < 1.

Application of phase field approach under 2D and 3D simulation for ductile fracture analysis

N. Khandelwal, A. Ramachandra Murthy — Wed, 05 Jun 2024 00:00:00 +0000

Phase Field (PF) theory is based on the variational principle and emerges as an efficient mathematical tool for numerical simulation of fracture behavior. The crack initiation and propagation solution within a unified mathematical model presents an added benefit to PF theory. PF formulation introduces two additional parameters: (1) phase field variable (ø) that discriminates the cracked and uncracked surface and (2) length scale parameter (L) converting the sharp crack into a diffusive crack. This paper investigates a comparison study of 2D and 3D Finite Element (FE) anaysis results using PF concept w.r.t ductile fracture. The mathematical formulation for the phase field method considering plasticity is carried out using AT1 and AT2 model. Numerical FE modelling is performed using ABAQUS software by considering quadrilateral element for 2D and hexahedral element for 3D simulations. Three standard benchmark examples were discussed in detail, and numerically predicted load-displacement results were compared with the results available in the literature. Further, the effect of L on crack behavior and loading capacity of the specimen is studied. The primary observation from the study states that an increase in the value of L, decreases the load carrying capacity and plastic dissipation of the material.

Singly curved shell element for applied element method

D. Lincy Christy, T.M. Madhavan Pillai, Praveen Nagarajan — Wed, 05 Jun 2024 00:00:00 +0000

Applied Element Method (AEM) is a numerical method which conventionally uses rectangular elements for structural analysis. AEM is advantageous because of its simplicity and faster processing. AEM can be used to track the collapse of structures. This method deploys the conversion of the structure into an assembly of rigid elements and flexible springs. Basically AEM has only two elements – two dimensional element and three dimensional (3D) element. Generally, 3D element is used for the analysis of 3D curved members which consumes more memory and processing time. For this, a shell element is necessary to represent the curved nature of the structure. This paper attempts to develop a singly curved shell element for AEM. The analysis of axisymmetric member illustrates the use of shell element. The effect of Poisson’s ratio normally neglected in rigid body methods is incorporated in this simplified shell element. The element developed is validated by both static and modal analyses. The results show that AEM is effective in predicting the behaviour of singly curved structures accurately.

A study of fly-ash and slag based alkali activated binder using sea water based alkaline activator

Tadicharla V.K. Ratna Bhanu, T.D. Gunneswara Rao — Wed, 05 Jun 2024 00:00:00 +0000

This paper presents investigation in alkali activated paste and alkali activated mortar produced by combinations of fly ash collected from coal based thermal power plant and ground granulated blast furnace slag collected from steel manufacturing facilities. The fly ash and ground granulated blast furnace slag are industrial by-products rich in aluminosilicates. The present study focuses on effect of utilization of seawater-based alkaline activator solution in alkali activated paste and mortar. Alkaline activator solution activates the chemical processes in binder materials when used in right concentrations and right proportion. This paper discusses the mechanical properties and microstructure characteristics of seawater-based alkali activated paste and mortar in comparison with conventional distilled waterbased alkali activator. The usage of sea water shown insignificant change in setting times and compressive strengths for various combinations of binder material. The microstructure analysis also showed less variation in mineralogical formations when conventional distilled water is replaced with sea water in preparation of alkaline activator solution.

Investigation on effectiveness of reinforced HSFRC overlay in flexural strengthening of RC beams

A. Kanchanadevi, Nawal Kishor Banjara, K. Ramanjaneyulu — Wed, 05 Jun 2024 00:00:00 +0000

At first, Hybrid Steel Fibre Reinforced Concrete (HSFRC) mixtures are developed and characterized for developing HSFRC overlay strips for flexural strengthening of Reinforced Concrete (RC) beams. HSFRC is developed using cement, sand and coarse aggregates of size 10 mm down, short straight-and long hooked-ended steel fibres in 1:3 proportion and densified silica fume to replace 7% by weight of cement. The fibre content is varied as 0.5, 1, 1.5 and 2% volume fraction. In order to assess the suitability of the HSFRC mixture developed for retrofit application, the mechanical and fracture characteristics of HSFRC are compared with that of plain concrete of same mixture proportion without fibres. Based on the merits, HSFRC with 1.5% volume fraction of fibres is chosen for the development of HSFRC overlay strips. The performance of a reinforced concrete beam after flexural strengthening with an innovative reinforced HSFRC overlay strip is compared with that of an unstrengthened control beam. Numerical model of RC beam retrofitted with reinforced HSFRC strip is developed and validated by comparing the results of numerical study with experimental results. A parametric study is carried out to evaluate the influence of thickness of overlay strip, level and strength of overlay reinforcement on the load carrying capacity and stiffness of the retrofitted beam. The parametric study brings out the potential of reinforced HSFRC overlay in flexural strengthening of RC beams and its ability to emerge as economic, feasible and promising retrofit strategy.

Performance evaluation of signal decomposition techniques for vehiclescanning- based modal identification of bridges

Appala Srinivas, K. Lakshmi, Voggu Srinivas — Wed, 05 Jun 2024 00:00:00 +0000

Indirect Structural Health Monitoring (SHM) otherwise known as vehicle-scanning method for bridge health monitoring is increasingly gaining importance due to the advantages such as the usage of single sensor on the moving vehicle without installing any sensors on the bridge, operation of traffic during vehicle-scanning, and better spatial resolution of the bridge due to moving sensor. The extraction of bridge frequencies, mode shapes, and damage using the drive-by method are posing few challenges due to the presence of roughness, measurement noise, and less transmissibility of thebridge characteristics. In order to obtain the bridge parameters and damage features, powerful signal processing tools are being relied on. One of the effective ways to perform feature extraction is through the decomposition of the signalinto useful components. In this paper, three signal decomposition techniques namely, Variational Mode Decomposition (VMD), Empirical Fourier Decomposition (EFD), and Singular Spectrum Analysis (SSA) which are robust in handling mode mixing and measurement noise are employed for extraction of bridge frequencies using the vehicle response. The performances of the three decomposition techniques are compared to evaluate their efficiencies for indirect SHM of bridges, using the drive-by vehicle. The comparative analysis is made and findings are obtained using the numerical simulation of a simply supported beam, with moving vehicle under varied speeds, road roughness, and measurement noise. The results of the numerical investigation show that the three techniques are efficient in decomposing the signal without mode mixing. It was found that, while the speed of the vehicle has no effect on the performance, measurement noise and roughness are affecting the effectiveness of the techniques. Also, SSA was found to outperform the other techniques in extracting the maximum number of mode shapes when compared to the other decomposition techniques from a noisy signal.

Vibration-based condition assessment of a steel structure under ambient excitation

Deepak Kumar, K. Lakshmi, V. Srinivas, A. Srinivas — Wed, 05 Jun 2024 00:00:00 +0000

Most of civil structures deteriorate with time due to many factors such as ageing, repeated loadings, wear-and-tear, lack of maintenance, and other environmental influences. While the structures are designed for strength, stability and deformation, the issues that are common are those of deterioration, durability and serviceability. Therefore, it is essential to assess the condition of the structures periodically if not continuously to prevent the deterioration leading to the decline of the strength, stability/serviceability. In real practice, the condition of structures is evaluated through condition assessment procedures. To evaluate the deterioration due to loss of stiffness, acceleration measurement which reflects the global information, is a great option when compared to strain, which needs a greater number of strain gages to capture the local information of a structure. In this paper, a method to evaluate the condition of a structure using acceleration responses is presented. The proposed technique is illustrated through an example of a steel building subjected to ambient excitations due to the operation of machinery. The technique is based on the updating of the Finite Element (FE) model of the structure, using the frequencies obtained from the measured acceleration response from the field. The frequencies obtained from the Modal analysis of the FE model are compared with the frequencies obtained from the field measurement. The dominant frequencies, excited with higher amplitudes in the field are found to be nearer to the FE frequencies but not the same. One of the main reasons for the difference is the change in the actual stiffness due to the deterioration of the member. This change or loss of stiffness is captured by updating the model with the frequencies of the field measured signal. Once the loss of stiffness is assessed, the current load-carrying capacity corresponding to the updated model is evaluated. The results of the studies from the steel building indicate the feasibility of the vibration-based technique for condition assessment. The proposed technique is able to identify the stiffness loss due to a reduction of the thickness of the column members by 9%, which is also verified using an ultrasonic thickness gauge in the field.

Experimental and numerical studies on the corrosion resistance and fatigue strength of short CFDST column

O.A. Farzana, R. Miji Cherian — Wed, 05 Jun 2024 00:00:00 +0000

Concrete Filled Double Steel Tube (CFDST) columns are composite columns consisting of concrete sandwiched between outer and inner steel tubes with a central hollow portion. CFDST members can be used in marine structures, bridges, high-rise viaduct piers, composite piles in offshore structures and high-rise buildings, due to their strength and stability. The performance of these composite structures is greatly affected by the corrosion of steel tubes. The present study aims at experimental and numerical investigations on the corrosion behaviour of Mild Steel - (MS)-CFDST column and Epoxy coated Galvonized Iron (GI)-CFDST columns. It also aims at to investigate numerically the fatigue behaviour of CFDST column under reversed cyclic loading using validated finite element model. A total of 6 specimens, three no. of MS-CFDST and epoxy coated GI-CFDST each were cast, and immersion corrosion testing was conducted for a time period of 60 days. The corrosion rate and failure pattern of the CFDST columns were determined. The fatigue strength of corroded CFDST columns were also evaluated by finite element modelling.

An experimental study on flexural performance of reinforced geopolymer concrete beams

S. Sundar Kumar, Md Adil Ahmed, V. Srinivasan, S. Maheswaran — Wed, 05 Jun 2024 00:00:00 +0000

Geopolymer concrete has emerged as a viable alternative to Portland cement concrete in recent years. Binders in geopolymer concrete are distinctively different from those in Portland cement concrete. The variation in properties of a geopolymer matrix can be high since the raw materials used are industrial wastes with essentially no control over their composition. This necessitates a complete characterization of the material as well as a thorough study of its mechanical, durability and structural properties. In this study, the flexural performance of reinforced geopolymer concrete beams designed as per Indian standards has been experimentally studied. The results though vindicate the use of geopolymer concrete in structural members, it has revealed that the structural behaviour of reinforced geopolymer concrete can distinctively differ from that of reinforced concrete beams made with Portland cement concrete. Results reported here indicate a reduced ductility in reinforced geopolymer concrete beams. Revision in the provisions of current concrete codes may be necessary. Relation between the properties of geopolymer concrete and the raw materials used in them needs to be thoroughly documented.