Concrete Armour Units Research Articles

Response of Dolos Concrete Armor Units to Impact Loads

A finite element analysis is conducted to determine the critical impact velocities for concrete dolos. The model formulation includes deformations at the contact surface and nonlinear material properties. Two dolos orientations are considered: vertical fluke seaward and horizontal fluke seaward. In both cases, the larger units fail at lower angular impact velocities. It is also shown that doubling the concrete strength increases the impact resistance by approximately 40 percent.

On the determination of concrete armour unit stresses including specific results related to Dolosse

Failures of rubble mound breakwaters armoured with complex types of unreinforced concrete armour units are often due to breakage. This happens when the stresses exceed the material strength. Sufficient parametric studies of the stresses are not yet available to produce design diagrams for structural integrity. The paper presents a general discussion of the problems related to stress determination and describes the results and the analyses of model tests with 200 kg and 200 g load-cell instrumented Dolosse. Static stresses, wave-generated stresses and stresses due to impacts were studied as well as model and scale effects. Moreover, some results from the Crescent City Prototype Dolosse study are presented and related to results from small-scale model tests. A preliminary design diagram for Dolosse is presented as well.

Deterministic computer-aided optimum design of rock rubble-mound breakwater cross-sections

The deterministic computation of the optimum rubble-mound breakwater cross-section is executed on a micro-computer. Moreover the application of CAD-software within the optimization process is examined. The quarry production, divided into a number of categories, and long-term distributions of deep water wave heights and water levels, form the basis of the computation. Deep water wave heights are converted to wave heights at site. A set of alternative cross-sections is computed based on both functional performance criteria, and Van der Meer's stability formulae for statically stable structures. Construction costs and maintenance costs are determined of each alternative. The optimum is derived by minimizing the sum of the construction costs and maintenance costs. Moreover, the programme provides means to economize the use of the quarry. At this stage the computer programme is useful for feasibility studies of harbour protection or coastal protection in regions, where use can be made of a quarry in the neighbourhood of the project site. Use of concrete armor units is excluded in this study. Concrete armor units are excluded sofar, but will be implemented in the next stage.

Rocking armour units: Number, location and impact velocity

As a part of a very extensive research on strength of concrete armour units model tests were performed on breakwater sections armoured with Cubes and Tetrapods. Stability tests resulted in a prediction of the number of moved units and the number of impacts as a function of wave height, period and location on the slope. Measurements on acceleration during impacts resulted in a description of the distribution of impact velocities at the centre of the unit. The expressions are applicable in prototype conditions.

Dynamic response of pre-stressed concrete armor units to pulsating loads

Concrete armor units are commonly employed for the protection of shorelines and rubble structures. Their design is based primarily on hydrodynamic stability. However, several recent breakwater failures indicate that unreinforced concrete armor units are susceptible to structural failure for hydraulically stable wave conditions. The structural stability of 42-ton dolos armor units, both unreinforced and pre-stressed and subject to wave-induced pulsating loads, are examined in this paper.

An Experimental Study on Dimensionless Linearized Friction Coefficient of Breakwaters with Precast Concrete Armour Unit

Linearized friction coefficient was examined experimentally for permeable breakwaters with precast concrete armour unit in shallow water region. The equation proposed by Sollitt et.al. was applied for calculating the friction coefficient from transmission coefficient. The friction coefficients obtained were less than 14 and varied with following parameters: ratio of incident wave height to block scale, HI/d, ratio of breakwater's width to wave length, B/L and wave steepness, HI/L. The parameter HI/d strongly affected the friction coefficient. The friction coefficient varied in the small range of 0 to 4 when the Reynolds number, ud/ v, was greater than 3×104.

Behaviour of steel-reinforced concrete armour units used in coastal defences

This paper reports on the use of steel reinforcement in slender-section concrete armour units used to protect the North Wirral coastline from storm erosion. The novel use of steel reinforcement has permitted the design of armour units that are both structurally and hydraulically more efficient than either natural stone armour or plain concrete armour units. However there is a risk that the steel reinforcement may suffer from corrosion attack within the design lifetime of the units. A programme of monitoring a sample of units on an annual basis has been established to assess their hydraulic, structural and durability performance. Electrical potential and resistivity methods are used to assess the level of corrosion activity in the steel reinforcement. A number of armour units have made use of cement replacements and admixtures in the mix design to enhance the durability characteristics of the concrete. The results of the initial four years of this study have shown that the armour units are behaving very well in all aspects of their performance. Furthermore, the use of steel reinforcement has permitted the full repair of accidental damage that would not have been possible with unreinforced concrete units.

Structural Modeling of Dolos Armor Units

The analysis of the structural integrity of a breakwater using concrete armor units in a physical model is presented for the first time. The key element in this analysis procedure is an instrumented dolos unit, which acts as a load measuring device. This load cell enables the primary generalized forces of moment and torque in the unit to be monitored when subjected to wave attach. A typical rubble-mound breakwater is designed for the analysis. A total of 36 tests are conducted, with the instrumented dolos unit placed at different locations within the breakwater armor layer. The test results show that, depsite the use of armor units that are stable under a single regular wave condition, structural failure could occur and, thus, demonstrate the inadequacy of the armor unit, as designed. Throughout the tests, the instrumented dolos performed with a high degree of reliability and sensitivity.

消波ブロック被覆堤ケーソンの波力と滑動に関する実験的考察

消波ブロック被覆堤ケーソンの波力と滑動に関する実験的考察

SIMPLIFIED MODELS FOR MEASURING ARMOUR UNIT FORCES

Damage of concrete armour units on a number of breakwaters around the world has brought into question the design methodology for these structures. The interaction of waves with a rubblemound breakwater is a complex process typified by the random nature of the wave loadings and of the placement and orientation of the armour units. The objective of this paper is to present the development of a more simplistic physical model for establishing a realistic upperbound for the forces occurring on concrete armour units, to more readily understand the response of the unit to various wave parameters, and to explore the effect of carrying out tests at different scales. The results of these investigations demonstrate the applicability of employing simplified models to assist in understanding the response of armour in a breakwater and the consistency of the instrumentation at different scales.

ANALYSIS OF 42-TON DOLOS MOTIONS AT CRESCENT CITY

Photogrammetry has been applied to make precise measurements of post-construction displacements of 38.2-metric ton (42-ton) dolosse on the outer breakwater at Crescent City, California. Data from two storm seasons are currently available from this monitoring program which was initiated in November 1986 and which is expected to continue at least through the next three winters. Supplemented by conventional land surveys, wave measurements, aerial inspections, and side scan sonar underwater imagery, observations from the photogrammetric monitoring have led to several preliminary conclusions regarding regions of relatively large dolos movement, dolos nesting, the dependency on breakwater slope of uprush or drawdown dominated armor unit movement, and the relative importance of armor unit movement and boundary conditions in dolos breakage. This paper describes the methods used for, and results obtained from, this monitoring effort along with the application of these results to a Corps study (Howell, 1988) Whose objective is to develop structural design criteria for the dolos concrete armor unit.

ARMOUR UNIT STRUCTURAL RESPONSE - A PARAMETRIC STUDY

There is a general lack of knowledge regarding the nature and magnitude of loads acting on armour units used for the protection of rubblemound coastal structures. Thus, a comprehensive design procedure incorporating both the hydraulic stability and the structural integrity of the armour units does not exist. This paper presents the results of a detailed parametric study of the structural response of armour units to wave-induced loading in a physical breakwater model. The effect of the following design parameters is investigated: breakwater slope, armour unit location, wave period and wave height. This research has made a number of significant contributions towards the development of a comprehensive design procedure for concrete armour units. It has identified a linear relationship between the wave-induced stress in the armour units and the incident wave height. In addition, it has shown that the conditional probability of waveinduced stress given wave height can be estimated by a log-normal distribution. Finally, a preliminary design chart has been developed which incorporates both the structural integrity and the hydraulic stability of the armour units.

QUALITY AND DURABILITY OF CONCRETE ARMOUR UNITS

The reliability of rubble mound breakwaters not only depends on the hydraulic stability but to a large extent on the strength of the armour units as well. In the debate on the shape of armour units, which turns out quite often to be merely academic in nature, generally too little attention is paid to the question of structural strength. On the occasion of the realization of the new outer harbour at Zeebrugge (Belgium) a serious effort has been made to arrive at a better understanding in the behaviour of concrete as construction material for armour units. This contribution gives an overview of the routine tests and of some particular investigations, carried out with respect to quality and durability of concrete armour units.

Dynamic response of dolos armor units

Concrete armor units are commonly employed for the protection of shorelines and rubble structures. Their design is primarily based on hydrodynamic stability, but their structural response to wave loading is poorly understood. In this study a wave force model is presented, which includes drag, inertia, kinetic and buoyant force components, to estimate hydrodynamic loads on the concrete armor unit, dolos. These loads are employed in a three-dimensional FEM analysis to determine the dynamic states of stress in a 42-ton dolos.

ON THE SCATTERING OF CONCRETE ARMOUR UNITS OF DETACHED BREAKWATERS DUE TO WAVES

On the Fuji Coast 15 detached breakwaters and 17 wave dissipating breakwaters have been constructed to prevent beach erosion. By virtue of the construction of the breakwaters the retreat rate of the shoreline position has decreased. However a large number of concrete blocks have been scattered due to waves. This study investigates the actual circumstances on the scattering of the concrete armour units of the detached breakwaters through the field observations on the Fuji Coast located in Suruga Bay facing the Pacific Ocean. The change rate of the plane area of the breakwater is examined from the aerial photographs, and the relationships among the parameter, the depth at the offshore foot of the breakwater and the number of the removed concrete armour units are investigated.

THE INFLUENCE OF OBLIQUE REFLECTION ON BREAKWATERS

The degree of reflection from rubble-mound breakwaters, even those comprising large pre-cast concrete armour units is greater than is usually thought. This is because the bulk of the face consists of smaller stones where water exchange in voids is minimal. Theory and experiment have shown that for 100% reflection of oblique waves the orbital motions are very complex, varying across the crest length of the short-crested system from rectilinear oscillation to circular or vortex motion. Also the influence of these high velocity orbital motions on a sedimentary bed have been shown to have a high scouring capacity. This has been exhibited in hydraulic models and in the field.

A PROCEDURE FOR THE ANALYSIS AMD DESIGN OF CONCRETE ARMOR UNITS

A rational approach to the design of rubble mound breakwaters that incorporates both the hydraulic stability and the structural integrity of individual concrete armor units is presented. A key element of this improved design procedure is the development of instrumentation to measure loads occurring on armor units in a physical model of a breakwater. Numerical methods have been employed to determine stresses throughout the armor unit once the loads are known and interaction design curves were developed from measured data. These interaction curves provide a useful assessment of the structural integrity of the armor units. The curves clearly demonstrate the overall factor of safety associated with the armor unit and the expected mode of failure. Based on the results of this type of analysis, the cost effectiveness and safety associated with different design alternatives may be explored and a breakwater that is both hydraulically and structurally efficient may be designed.

Use of Grout‐Filled Sausages in Coastal Structures

An alternative to rubble mound construction, with or without precast concrete armor units, is recommended which comprises flexible membranes filled with cement mortar in situ. The placement of these for greatest stability is suggested by maximizing surface contact of sausage type units. Results of tests to derive an economical mortar mix are described. Construction details are outlined together with comparative costs for a marina breakwater.

Nonlinear dynamic analysis of concrete armor units

Concrete armor units are commonly employed for the protection of shorelines and rubble structures. Their design is primarily based on hydrodynamic stability, but their structural response to wave loading is poorly understood. In this study, a simple model is presented to estimate impact loads due to wave slamming on the concrete armor unit, dolos. A nonlinear dynamic analysis indicates that the units will experience a structural failure at hydrodynamically stable wave conditions.

Concrete Armor Unit Forms Inventory

Concrete armor units in many shapes are currently being used to protect coastal structures. A significant percentage of the unit's manufacturing cost is the cost of the form. Forms for manufacturing dolosse, tribars, tetrapods, sta-pods, and sta-bars may be obtained from private industry with an inventory and private companies which build forms. Also, some U.S. Government agencies have forms available for their agency use only. Private industry with available forms are located in the Virgin Islands, the states of Oregon, California, and Hawaii, and in Quebec, Canada. Private companies which build forms for sale are located in the states of New York, Iowa, Texas, and Oregon.