1- Introduction

2- Bridge description

3- Bridge instrumentation

4- Test procedure

5- Field test results

6- Finite element analysis

7- Summary and conclusions

References

Abstract

Many steel bridges in the United States designed before the mid-1980s are highly susceptible to distortion-induced fatigue cracking. This vulnerability is substantially increased if the out-of-plane driving force caused by differential girder displacement is increased for any reason. This research examines one such case where a double-deck bridge complex, originally built in the 1960s, was retrofitted to improve seismic performance. As part of the retrofit, single angle K-type diaphragms were replaced with stiffer double-angle cross-type diaphragms. This seismic retrofit led to an increase in web-gap stresses, and within approximately one year following the retrofit, inspectors identified numerous fatigue cracks in the web of longitudinal girders where connection plates terminate near top flanges. A repair measure was implemented to provide a positive connection between the connection plate and the girder flange. The purpose was to reduce the high stress concentrations in the web-gap region by restricting the out-of-plane distortion in the web-gap region. Field tests were carried out in addition to developing finite element (FE) models to investigate the efficacy of the repair technique. The results confirmed a significant decrease in the web-gap stress after implementation of the repair, and a subsequent FE analysis showed that the new load path through the repair angle section did not introduce a new fatigue sensitive area. In fact, the repair resulted in stresses well below the constant amplitude fatigue threshold (CAFT) for this type of detail.

Introduction

Most continuous-span double-deck viaducts built in the San Francisco Bay Area during the 1950s and 1960s were damaged during the 1989 Loma Prieta earthquake [1]. The deficiencies in these viaducts led to an immediate review of all double-deck bridge structures in the United States. One particular seismic retrofit project (and the focus of this work) involved a Midwestern double-deck bridge complex with substructure and superstructure elements without adequate capacity based on current seismic criteria [2,3]. A seismic retrofit strategy was adopted based on the criteria described in the FHWA Seismic Retrofitting Manual for Highway Bridges [4]. Almost immediately following completion of the seismic retrofit, horseshoe-shaped cracks were identified in the unstiffened regions (frequently called the web gap) of the longitudinal girders where the original K-type diaphragms were replaced with new, stiffer cross-diaphragms. This problem mostly occurs in bridges built in the United States prior to the mid-1980s when the design specifications required connection plates to have a tight-fit detail at the girder flanges, but not welded [5–7]. Normally, part of the connection plate, attached to plate girders, must be clipped to clear the web-to-flange weld resulting in a soft and short section that is more flexible in the transverse direction than the rest of the girder’s height. This area in the web is known as the web-gap region. Cracks originating in this region are likely the result of secondary stresses resulting from out-of-plane distortion in the unstiffened web-gap region and account for approximately 90% of all fatigue cracking [23]. As a result, a significant number of older bridges have been affected by distortion-induced fatigue cracking in the web-gap region.

The waste problem is a problem faced throughout the world. This research aims to save the environment with on the utilization of recycling waste materials that do not contribute much in people’s lives over the years. Organic cement is an alternative cement besides portland cement made from organic waste recyled and substitution of mediteran soil. The research is oriented to chemical compounds, compressive strength, and tensile strength testings of concrete by using organic and portland cements. Age of concrete in the research are 3, 4, 14, 21, and 28 days old. Result for compressive test of cylinder concrete with organic cement, it obtained 6.10 MPa while the cylincer concrete with portland cement, it obtained 20.22 MPa. For tensile strength test of cylinder concrete with organic cement on 28-days-old concrete reached 1.09 MPa and those with portland cement reached 2.01 MPa. From the physical test result, it obtained the density of organic cement is 3.01 gr / ml, while for the density of portland cement is 3.16 gr / ml. From the analysis of organic cement chemical compounds through laboratory testing methods result, it found indications that resemble portland cement chemical compounds that are CaO;65,36%, SiO₂; 18,84%, Al₂O₃; 6,33%, Fe₂O₃; 2,29%, SO₃ ; 3,64%, MgO; 1,35%, C₃S; 66,72%, C₂S; 3,98%, C₃A; 12,9%, and C4Af; 6,97%.

Introduction

Currently, the waste problem is a problem faced throughout the world. Gradually, the high volume of waste has a negative impact on the environment. Handling of waste management is necessary because of the huge negative impact that can be generated. The waste problem seems not a simple matter, as long as there is human life then the problem will always arise. Urban waste management in Indonesia is a real problem as population growth has an impact on increasing the amount of waste and the occurrence of aesthetic degradation problems around landfills that have potential to cause social conflict with surrounding communities. [1]. Along with economic growth, per capita garbage production will continue to increase so it can be predicted in 2030 will reach 1,2 kg / capita / day for urban areas and 0,55 kg / person / day for rural areas. In Indonesia, organic waste is a major component of waste. The proportion of organic waste is between 34-70% which is 20-30% higher than most countries in Europe [2]. The high growth of waste volume coincides with high population growth rate. Therefore, the current waste problem can be said to be a world problem. In addition, with good handling and good waste management, environmental savings have been made.Handling of organic waste through the combustion process with the furnace at 700° C to ashes will contain elements of 69.7% CaCo3, 12.1% KCl; 3% SiO2, 8.1% Fe and 3% Al2, while shellfish ash contains 100% CaCo3 [3]. Therefore, in dealing with it, it is deemed necessary to find the best solution to resolve current waste problems. This research aims to save the environment with emphasis on the utilization-oriented form of recycling waste materials that do not contribute much in people’s lives over the years.This research is a renewable research to obtain alternative building materials, especially alternative cement in addition to portland cement which has been used in public life. The increase in cement growth is still influenced by the high level of private sector development and the high demand for housing for the community [4]. The increasing demand for housing and infrastructure automatically demands the need for building materials that are also increasing.The need for building materials must be overcome with the use and discovery of building materials that can provide an alternative [5]. Organic cement is the newest alternative cement in addition to portland cement made through organic waste recycling systems and by substitution of mediteran soil [6]. The development of the use of alternative sources for the manufacture of cement has also been developed by Japan which has been producing eco-cement made from city ash waste through combustion in lieu of some of the main raw materials containing 50% of cement raw materials such as sewage sludge [7]. To create Eco-Cement CSA Clinker,the appropriate starting raw material needs to be burned at a maximum temperature of 1200-1300 ° C. Reuse of waste materials in the form of phosphogypsum will reduce the temperature and time of the combustion process. Large scale eco-cement making can be done in conventional furnace used for portland cement and produce chemical cement mineralization of C = CaO, A = Al2O3, S = SiO2, s = SO3, F = Fe2O3, M = MgO, Ye’elimite 4CaO, 3Al2O3, SO3 and C4A3s [8]. Mediteran soil is a soil formed from weathering of sedimentary rock and limestone. This type of soil contains a considerable amount of carbonate and other compounds of iron, water, aluminum, and some other organic materials [9].

1- Introduction

2- Problem definition and theoretical framework

3- Cohesive-frictional soil (γ ≠ 0, c ≠ 0, ϕ ≠ 0)

4- Purely cohesive soil (γ ≠ 0, c = cu, ϕ = 0)

5- Summary of results and ultimate failure envelopes

6- Conclusions

References

Abstract

The seismic bearing capacity of shallow foundations is affected by inertia forces acting both on the structure and in the supporting soil. Even though the former have been recognised to play often the major role, by increasing the horizontal load and the overturning moment transferred to the foundation, both of them must be taken into account in the seismic design of foundations. Using a pseudostatic approach and based on the upper bound theorem of limit analysis, a comprehensive set of formulas is derived for the computation of the seismic bearing capacity of strip footings resting on cohesive-frictional and purely cohesive soils. Results are given in terms of: (i) reduction coefficients for the Terzaghi’s equation of the vertical bearing capacity and (ii) ultimate failure envelopes in the space of normalised loading variables. These formulas extend to more general conditions other literature results, allowing to take into account easily the effects of inertia forces acting both on the superstructure (load inclination and eccentricity) and into the foundation soil. The reliability of the proposed equations, suitable for the design practice, is verified through a thorough comparison with other rigorous and approximate solutions.

Introduction

Many studies on the seismic bearing capacity of shallow foundations have shown that inertia forces acting on the structure and in the supporting soil tend to reduce the bearing capacity under seismic conditions. Most works on this topic have been carried out with a pseudostatic approach [18,22,23,25,3,29,30,32,34,35,5,6,9], by adopting: (i) different methods (numerical or theoretical) and theories (limit equilibrium, limit analysis or method of characteristics); (ii) different constitutive assumptions for the soil (purely frictional, purely cohesive or cohesive-frictional); (iii) different hypotheses on the inertia forces on the soil (with or without the vertical component) and (iv) on the structure (equal to or a fraction of those acting on the soil). Despite the fact that structure inertia has been recognised to play often the major role in reducing the seismic bearing capacity of shallow foundations, recent studies have highlighted possible situations in which even the effects associated to soil inertia can have a significant relevance, in the case of either frictional [22,6] or purely cohesive [24] soils. Moreover, most design codes recommend to take into account the effects of soil inertia in the seismic design of such systems (e.g.: [10]). Going to the design practice, the bearing capacity of shallow foundations under general loading is usually evaluated by means of simple approaches, neglecting any possible soil-structure interaction effect. In this context, codes and guidelines make use of closed form expressions for the bearing capacity, given in the form of either the classical Terzaghi’s formula [1,17] or complete three-dimensional failure envelopes [10]. With this respect, only few works in the literature provide empirical formulas including inertia forces both on the structure and into the soil. As far as spread footings on cohesive-frictional soils are concerned, Budhu and Al-Karni [3], Paolucci & Pecker [23] and Cascone et al. [5] provide reduction factors for the vertical bearing capacity. However, Budhu and Al-Karni [3] consider the same accelerations into the soil and the structure; Paolucci & Pecker [23] do not contemplate the effects of the structure inertia on the Nc and Nq bearing capacity factors, while Cascone et al. [5] refer only to the effects of the seismic action on the Nγ term, thus resulting in a limited applicability of the proposed formulas. Only very recently, Cascone & Casablanca [6] proposed empirical expressions for the reduction coefficients, derived from the best fit of numerical results.

The bearing capacity of foundations on soft clays under undrained conditions has been computed with inclusion of (i) a single vertical granular trench below a strip footing and (ii) a granular column placed below a circular footing. A lower bound plane strain and axisymmetric limit analysis, in conjunction with finite elements and an optimization procedure, has been used. The efficiency factor (n) has been determined by varying Bt/Bf; where (i) Bt = diameter of the column (width of the trench) and (ii) Bf = diameter of the circular footing (width of the strip footing). The effect of (i) the depth (D) of the column (trench) and (ii) the angle of internal friction (/) of the column (trench) material has been explored for a wide range of cu/(cBf); cu and c imply undrained cohesion and the unit weight of the clay mass, respectively. Factor n increased quite significantly with increases in Bt/Bf and D/Bf. Factor n improved further with (i) increases in / and (ii) decreases in cu/(cBf).

Introduction

A number of investigations, that examined the improvement in the bearing capacity of foundations by the insertion of granular trenches and columns, have been reported in literature. The studies are based on (i) analytical approaches (Madhav and Vitkar, 1978; Bouassida and Hadhri, 1995; Bouassida et al., 1995), (ii) elasto-plastic finite element analyses (Schweiger and Pande, 1986; Mitchell, 1985), and (iii) numerical lower and upper bound finite element limit analyses (Bouassida et al., 2015). Series of small-scale model experiments (Hamed, 1986; Nazir and Azzam, 2010; Bouassida and Porbaha, 2004) and full-scale field tests (Mitchell, 1981, 1985; Stuedlein and Holtz, 2012) have been carried out by a few researchers. These different model and field tests revealed that the bearing capacity of foundations can be increased quite significantly with an increase in the depth of the granular trench. In the present paper, the aim is to determine the bearing capacity of both strip and circular footings, placed on soft to medium soft clays reinforced with a single granular trench and column, respectively, by using the lower bound limit analysis with finite elements and the optimization principle.

The bearing capacity of saturated soils can be estimated by extending either the effective stress approach (ESA; Terzaghi, 1943) or the total stress approach (TSA; Skempton, 1948). Criterion for determining appropriate approach between the ESA and the TSA are based on the soil type and drainage condition of pore-water during the loading stages. Shallow spread footings are commonly used as foundations of light structures. In many cases (especially in arid and semi-arid regions), the water table is relatively deep, and the pressure bulb typically lies within the vadose zone where soils are in unsaturated condition with negative pore-water pressure. Soil desaturation associated with lowering the natural ground water level or water evaporation from the soil surface results in an increase in the bearing capacity compared to the saturated soil condition. Various research related to the bearing capacity of unsaturated soils suggest that this increase can be attributed to the influence of soil suction (Broms, 1964; Steensen-Bach et al., 1987; Fredlund and Rahardjo, 1993; Oloo et al., 1997; Costa et al., 2003; Rojas et al., 2007; Balzano et al., 2012). Nevertheless, there are still uncertainties as to which approach (i.e. ESA or TSA) is more appropriate in the reliable estimation of the bearing capacity of unsaturated soils. Vanapalli and Mohamed (2007) and Schanz et al. (2011) showed that the bearing capacity of unsaturated sandy soils can be reliably estimated extending the ESA taking account of the influence of matric suction. Oh and Vanapalli (2013a) conducted model footing tests in unsaturated glacial till (i.e. Indian Head till) and concluded that the TSA based on the unconfined compressive strength of unsaturated soils can provide a more reasonable bearing capacity of unsaturated cohesive soils. These research studies related to the bearing capacity of unsaturated cohesionless and cohesive soils indicate that the bearing capacity of unsaturated soils should be estimated considering the type of soil and the drainage conditions of pore-water and poreair. The ESA and the TSA for unsaturated soils are designated as the modified effective stress approach (MESA) and the modified total stress approach (MTSA), respectively. In-situ plate load test (PLT) is one of the most reliable testing techniques for estimating the bearing capacity of shallow foundations. In-situ PLTs are typically carried out on soils that are in a state of unsaturated condition; hence, there are uncertainties in analyzing the in-situ PLT results in terms of scale effect and matric suction distribution profile with respect to depth (Oh and Vanapalli, 2013b). For this reason, numerical analysis is commonly used as an alternative to the in-situ PLTs to estimate the bearing capacity of unsaturated soils.

Purely viscous dampers are devices that can be used in bracing systems to dissipate large part of input seismic energy [1,2]. They consist of a cylinder, filled with a silicone fluid inside which a piston slides, allowing the device to produce a force F c sign u u =⋅ ⋅ ( ̇) ̇ α, where c is the damping constant characteristic of the device, u̇ is the velocity between the two device ends and α is an exponent typical of the device type. Optimisation of linear viscous damper systems (i.e. α = 1) has been widely studied in the literature (see for instance [3–5]). In comparison, nonlinear devices have been investigated in less works, due to inherent difficulties in the analytical formulation. In [6], a simplified procedure for damper design aimed at a given target in terms of displacement reduction factor was developed. Reference [7] proposes a practical method for optimum design of non-linear oil dampers with relief mechanism. A comprehensive probabilistic design methodology considering life-cycle cost criteria together with uncertainty in structural response and earthquake loading is proposed in [8]. Most of these methods rely on simplified assumptions that may limit their use, i.e. very specific objectives, reduction of the structure to simpler SDOF systems, linearization of damper behaviour, limitation of design variables. However, any designer knows that objectives and constraints are often given by the specific problem at hand, and thus a flexible procedure which can be adapted to the case under study may be more desirable than more efficient yet problem-dependent methodologies. In this work, an optimisation-based approach to the design of nonlinear viscous dampers for seismic retrofitting of frame structures is investigated. Different objectives and constraints are proposed to show the flexibility of the methodology, and comparisons with state-of-theart methods of the literature are provided.

Besides seismic base isolation [1,2] and other strengthening techniques [3], the use of fluid viscous dampers (FVDs) as energy dissipation devices has rapidly increased in the last few years [4] for seismic retrofitting of existing civil engineering structures. Their appealing properties include the large energy dissipation capability, the low maintenance required, and the generation of forces that are out of phase with the elastic forces, thereby not increasing the stress in the structure. Experimental evidence [5–9] reveals that the constitutive behavior of FVDs can be described by a fractional velocity power law f = cu u | | sgn( ̇ ̇) NL α d d (1) where cd is the damping coefficient, α is a velocity exponent, u̇ represents the relative velocity at the ends of the device and sgn(⋅) is the signum function. The exponent α is responsible for the nonlinear damping of FVDs and depends upon the hydraulic circuit employed. Typically, α ranges from 0.10 to 0.50 for seismic applications. As a result of the nonlinear constitutive behavior of FVDs, linear methods of analysis, e.g., the response spectrum method, are no longer applicable. In this regard, attempts have been made to determine an equivalent viscous damping ratio due to the added nonlinear FVDs [10], or an equivalent damping coefficient of energy-equivalent FVDs associated with the same energy dissipation as the nonlinear FVDs [11]. The above-mentioned relationships, extremely useful for preliminary design purposes, are amplitude-dependent due to the nonlinear nature of FVDs. Furthermore, they are strictly valid under the hypothesis of harmonic motion. Since the earthquake-induced motion is not really harmonic but is generally modelled as a random process, the estimation of the equivalent damping coefficient can be alternatively performed within the framework of the stochastic linearization technique (SLT) [12]. The SLT was applied in a number of research papers and to a general class of nonlinear behaviors, not just confined to the one shown in (1), e.g.: in the context of tuned liquid column damper optimization [13,14], characterized by quadratic-times-signum-like damping; in the field of nonlinear energy sinks optimization [15], featured by a cubic stiffness; for optimizing the performance of hysteretic dampers [16], represented by a Bouc-Wen model. The SLT has also been successfully applied to derive equivalent linear properties of bilinear systems [17,18] in the framework of response spectrum analysis [19,20]. Coming back to the nonlinearity of FVDs given by (1), which is of interest to the present note, in the literature the SLT has been applied by introducing the stochastic nature of the earthquake input via a powerspectral-density (PSD) function S ω ü ( ) g , for example the Kanai-Tajimi PSD [21–23], or a particular spectrum-compatible PSD function [24,25]. All these quoted papers used a popular force-based Gaussian SLT (F-G-SLT). In this note, it is demonstrated that this variant of SLT is not the best option for the kind of nonlinearity induced by the FVDs. After a critical assessment of six alternative formulations of SLT, we identify a so-called equal-energy non-Gaussian SLT (EE-NG-SLT) that, without increased computational effort, is better able to capture the nonlinear response of the system.

Countries and cities have been faced with major increasing problems with the disposal of recycled materials, such as rubber, glass, and plastics for several years. The consumption of the world’s rubber has nearly reached 24.9 million tons in year 2010. In the U.S. alone, approximately 3.9 million tons of scrap tires are produced every year, out of which 1.36 million tons are recycled and 2.54 million tons are burned or land-filled. In view of the wide and vast market for scrap tires, about a quarter of all scrap tires end-up in landfills numbering to approximately 27 million tires or roughly 6 million tons annually, making-up over 12% of all solid waste. The disposal of the scrap tires materials become very costly once they are sent to landfills; not to mention the wide space that they use in landfills to dispose of, and the hazard that they cause towards the environment. Based on this information, the rubber use in concrete and pavement material provides an environmentally sustainable method for disposing of the millions of tires that are annually generated. Powdered rubber is a general term or an expression given to recycled rubber that is generated from scrap tires. The production of powder rubber consists of removing the steel and fluff, then using a granulator and/or cracker mill, with the aid of cryogenics or mechanical means, in order to reduce the size of the tire particles. A well-known fact is that tires can be divided into two major groups: automobile tires and truck tires, and they are different from each other. The description of the rubber source is very important and should always be specified in the literature because it has an influence on the texture and the shape, and consequently, on the characteristics of the concrete that is adjusted by the addition of the specified percentage of the rubber. It is also important to point out that automobile tires and truck tires vary not only in shape, weight and size, but above all, in the ratio of the components of the base mixture. Researchers have considered three wide categories of discarded tire rubber concrete mix design:

1. Chipped Rubber: This type of rubber has dimensions of about 25 to 30 mm and used to replace the coarse aggregates in concrete.

2. Crumb Rubber: The particles of rubber are highly irregular, varying between 3 to 10 mm, and are used to replace the fine aggregates.

3. Powdered Rubber: The particles of the rubber are smaller than 1 mm and consist of the powder formed during the crunch process, fallen from the machinery of the plant that is handling the waste rubber. This type of rubber could be used as filler in concrete due to its size.

1. Introduction

Red mud is an inorganic residue generated during the industrial production of alumina by the Bayer process. Red mud is classified as a toxic waste with elevated disposal costs due to the high basicity and leaching potential [1]. An annual world production of 21 million tons of aluminum corresponds to 82 million tons of red mud waste, so that new applications of this industrial residue are urgently needed. Construction materials such as cements, lightweight aggregates and geopolymers are considered interesting solutions for red mud safe disposal [2]. The term ‘geopolymer’ identifies an alumino-silicate material with distinctive environmental advantages compared to ordinary Portland cement. The synthesis involves the dissolution of alumino-silicate raw materials in an alkaline medium, followed by condensation and polymerization to achieve a highly stable three-dimensional network structure, where AlO4 and SiO4 are linked together sharing oxygen ions. The network has the capability to immobilize possible pollutants when wastes (usually industrial residues) are used as alumino-silicate source [3]. Red mud has been already proposed as raw material in geopolymer production, but always with a supplementary Al source, such as metakaolin [4] or fly ash [5], mainly to enhance the mechanical strength of the products. The present study aimed to use red mud as the only Al source and to eliminate the use of relatively expensive Na-silicate activating solution. This was supported by the use, as silica source, of soda lime glass (SLG) from urban waste collection. The specific waste glass fraction employed, where plastic and ceramic impurities are concentrated, is currently mostly landfilled [6].

2. Materials and methodology

Red mud (RM) with chemical composition: SiO2=5.21%, Al2O3=15.21%, Fe2O3=52.94%, CaO=2.95%, Na2O=2.40%, K2O=0.63wt.% (Gardanne, France) and soda lime glass (SLG) (SASIL S.p.a, Biella, Italy) with hemical composition: SiO2=70.50%, Al2O3=3.20%, Fe2O3=0.42%, CaO=10.00%, Na2O=12.00%, K2O=1.00 wt.%. were dissolved in NaOH solution of desired concentration (4M and 6M) [7]. The SiO2/Al2O3 theoretical molar ratio of the final geopolymers was fixed at 5, 6 and 7, which represents initial mixtures of SLG/RM in wt.% of 40/60, 45/55, 50/50, respectively. The sample designation was established as xSyM, where “x” is associated with the SiO2/Al2O3 molar ratio, “y” refers to the molarity of the activating solution, varying from 4M to 6M. The liquid to solid ratio was fixed at 0.50 for all mixtures. Geopolymer samples were prepared by mechanical mixing waste glass and red mud in a sodium hydroxide solution for 4 hours before being casted in cylindrical polyethylene moulds, cured at 75°C for 10 days. The compressive strength was measured by using an Instron 1121 UTS (Danvers, MA) testing machine, operating with a cross-head speed of 0.5 mm/min. 10 cylindrical samples, with diameter of 14mm and height of 20mm, were tested for each batch. Microstructural evaluation was performed by means of scanning electron microscopy (SEM) (LEO 435 VP, Cambridge, UK and Ultra Plus, Zeiss, Jena, Germany), equipped with EDX. Solid-state Magic Angle Spinning (MAS) NMR spectra were recorded on an Agilent DD2 500WB spectrometer equipped with a commercial 3.2 mm triple resonance MAS probe at 27Al resonance frequency of 130.24 MHz. The heavy metal release was evaluated according to the European Standard for waste toxicity evaluation (EN 12457-2) and analysed using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) (SPECTRO Analytical instruments GmbH, Kleve, Germany).