阅读说明：本技术 基于分布式光纤技术的桥梁有效预应力监测方法 (Bridge effective prestress monitoring method based on distributed optical fiber technology ) 是由 叶仲韬 谢山海 肖金军 邓潼 罗国民 黄信明 胡俊亮 刘凯 梅秀道 郭翠翠 王金 于 2021-08-03 设计创作，主要内容包括：本发明涉及一种基于分布式光纤技术的桥梁有效预应力监测方法,其包括以下步骤：在待监测桥梁的底部沿纵向布置分布式应变光纤；使车辆驶过所述待监测桥梁,计算所述待监测桥梁的测点在监测初期活载与恒载共同作用下的应力σ-(1)；同时根据所述分布式应变光纤采集得到测点的初始应变时程曲线,计算所述测点的初始峰值应力σ；使所述车辆每隔预设时间驶过所述待监测桥梁,根据所述分布式应变光纤采集得到所述测点的实时应变时程曲线,计算所述测点的实时峰值应力σ’；根据所述活载与恒载共同作用下的应力σ-(1)、初始峰值应力σ和实时峰值应力σ’计算得到所述测点的预应力损失Δσ。以解决相关技术中智能化不足、精度不高、长期稳定性差、很难全面监测的问题。(The invention relates to a method for monitoring effective prestress of a bridge based on a distributed optical fiber technology, which comprises the following steps: arranging a distributed strain optical fiber at the bottom of a bridge to be monitored along the longitudinal direction; enabling a vehicle to drive through the bridge to be monitored, and calculating the stress sigma of a measuring point of the bridge to be monitored under the combined action of live load and constant load at the initial monitoring stage 1 (ii) a Meanwhile, acquiring an initial strain time-course curve of the measuring point according to the distributed strain optical fiber, and calculating an initial peak stress sigma of the measuring point; enabling the vehicle to drive through the bridge to be monitored at preset time intervals, acquiring a real-time strain time course curve of the measuring point according to the distributed strain optical fiber, and calculating the real-time peak stress sigma' of the measuring point; according to the stress sigma under the combined action of the live load and the dead load 1 And calculating the initial peak stress sigma and the real-time peak stress sigma' to obtain the prestress loss delta sigma of the measuring point. The problems of insufficient intellectualization, low precision, poor long-term stability and difficulty in comprehensive monitoring in the related technology are solved.)

1. A bridge effective prestress monitoring method based on a distributed optical fiber technology is characterized by comprising the following steps:

arranging a distributed strain optical fiber at the bottom of a bridge to be monitored along the longitudinal direction;

enabling a vehicle to drive through the bridge to be monitored, and calculating the stress sigma of a measuring point of the bridge to be monitored under the combined action of live load and constant load at the initial monitoring stage₁(ii) a Meanwhile, acquiring an initial strain time-course curve of the measuring point according to the distributed strain optical fiber, and calculating an initial peak stress sigma of the measuring point;

enabling the vehicle to drive through the bridge to be monitored at preset time intervals, acquiring a real-time strain time course curve of the measuring point according to the distributed strain optical fiber, and calculating the real-time peak stress sigma' of the measuring point;

according to the stress sigma under the combined action of the live load and the dead load₁Calculating initial peak stress sigma and real-time peak stress sigma' to obtain the measured pointThe prestress loss Δ σ.

2. The method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology according to claim 1, wherein:

the stress sigma under the combined action of the live load and the dead load₁Calculating the initial peak stress sigma and the real-time peak stress sigma' to obtain the prestress loss delta sigma of the measuring point, wherein the prestress loss delta sigma of the measuring point comprises the following steps:

calculating the initial stress sigma generated on the beam bottom by the prestress action at the initial monitoring stage₂And real-time stress sigma generated at the bottom of the beam by prestress action at preset intervals₂', the prestress loss Δ σ is calculated according to the following formula:

Δσ＝σ₂-σ₂'

3. the method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology as claimed in claim 2, wherein:

the initial stress σ₂And real time stress sigma₂The calculation method of' is as follows:

σ₂＝σ-σ₁

σ₂'＝σ'-σ₁

where σ is the initial peak stress, σ' is the real-time peak stress, σ₁The stress under the combined action of live load and constant load.

4. The method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology as claimed in claim 2, wherein:

stress sigma under the combined action of the live load and the dead load₁After the initial peak stress sigma and the real-time peak stress sigma' are calculated to obtain the prestress loss delta sigma of the measuring point, the method further comprises the following steps:

and calculating the residual rate mu of the prestress effect of the measuring point according to the prestress loss delta sigma.

5. The method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology as claimed in claim 4, wherein:

the calculation method of the residual rate mu of the prestress effect comprises the following steps:

6. the method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology according to claim 1, wherein:

the step of obtaining an initial strain time-course curve of the measuring point according to the distributed strain optical fiber collection, and the step of calculating the initial peak stress sigma of the measuring point comprises the following steps:

extracting initial peak strain epsilon according to the initial strain time course curve, and calculating the initial peak stress sigma according to the following formula:

σ＝εE

wherein E is the elastic modulus of the concrete.

7. The method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology according to claim 1, wherein:

the step of obtaining a real-time strain time-course curve of the measuring point according to the distributed strain optical fiber acquisition, and the step of calculating the real-time peak stress sigma' of the measuring point comprises the following steps:

extracting real-time peak value strain epsilon 'according to the real-time strain time course curve, and calculating the real-time peak value stress sigma' according to the following formula:

σ'＝ε'E

wherein E is the elastic modulus of the concrete.

8. The method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology according to claim 1, wherein:

stress sigma under combined action of live load and constant load₁The calculation method comprises the following steps:

wherein M is₁For the moment of bending, M, caused by the dead load of the bridge to be monitored₂Bending moment, y, caused for said vehicle live load₁Is the distance, y, between the bottom of the bridge to be monitored and the inertia axis of the vehicle₂The moment of live load effective stress of the vehicle, and I is the moment of section inertia of the bridge to be monitored.

9. The method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology according to claim 1, wherein:

the longitudinally arranged distributed strain optical fiber at the bottom of the bridge to be monitored further comprises:

and arranging a distributed temperature optical fiber at the bottom of the bridge to be monitored along the longitudinal direction, connecting the tail parts of the distributed temperature optical fiber and the distributed strain optical fiber in series, and respectively connecting the end parts of the distributed temperature optical fiber and the distributed strain optical fiber into an optical fiber demodulator.

10. The method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology according to claim 1, wherein:

and at the initial monitoring stage and every preset time, when the environment temperature of the bridge to be monitored, which is measured by the distributed temperature optical fiber, is T, the vehicle is driven across the bridge to be monitored.

Technical Field

The invention relates to the field of prestressed concrete bridges, in particular to a method for monitoring effective prestress of a bridge based on a distributed optical fiber technology.

Background

Compared with the common concrete beam type bridge, the prestressed concrete beam type bridge has the advantages of greatly improving the span, the bearing capacity and the durability, and having very obvious cost advantage compared with a steel bridge, so that the prestressed concrete beam type bridge exists in China in a large number. The prestressed concrete bridge has the reactions of shrinkage creep and the like, so that the prestressed loss is caused, the structure generates defects such as downwarping, cracks and the like, the structural performance is further degraded, the prestressed loss condition of the prestressed concrete beam bridge is mastered, and the method has important significance for evaluating the bridge performance and ensuring the safe operation of the bridge.

In the related technology, the prestress detection mode of an operating bridge mainly comprises the steps of sticking a strain gauge on a steel strand for measurement; arranging a pressure sensor at the end of the steel strand for measurement; the method for measuring the strain sensors arranged on the beam has the problems of insufficient intellectualization, low precision, poor long-term stability, difficulty in comprehensive monitoring and the like.

Disclosure of Invention

The embodiment of the invention provides a method for monitoring effective prestress of a bridge based on a distributed optical fiber technology, which aims to solve the problems of insufficient intellectualization, low precision, poor long-term stability, difficulty in comprehensive monitoring and the like of the existing related detection method.

In a first aspect, a method for monitoring effective prestress of a bridge based on a distributed optical fiber technology is provided, which comprises the following steps: arranging a distributed strain optical fiber at the bottom of a bridge to be monitored along the longitudinal direction; enabling a vehicle to drive through the bridge to be monitored, and calculating the stress sigma of a measuring point of the bridge to be monitored under the combined action of live load and constant load at the initial monitoring stage₁(ii) a Meanwhile, acquiring an initial strain time-course curve of the measuring point according to the distributed strain optical fiber, and calculating an initial peak stress sigma of the measuring point; enabling the vehicle to drive through the bridge to be monitored at preset time intervals, acquiring a real-time strain time course curve of the measuring point according to the distributed strain optical fiber, and calculating the real-time peak stress sigma' of the measuring point; according to the stress sigma under the combined action of the live load and the dead load₁And calculating the initial peak stress sigma and the real-time peak stress sigma' to obtain the prestress loss delta sigma of the measuring point.

In some embodiments, the stress sigma under the combined action of the live load and the dead load is determined₁Calculating the initial peak stress sigma and the real-time peak stress sigma' to obtain the prestress loss delta sigma of the measuring point, wherein the prestress loss delta sigma of the measuring point comprises the following steps:

calculating the initial stress sigma generated on the beam bottom by the prestress action at the initial monitoring stage₂And real-time stress sigma generated at the bottom of the beam by prestress action at preset intervals₂', the prestress loss Δ σ is calculated according to the following formula:

Δσ＝σ₂-σ₂'

in some embodiments, the initial stress σ₂And real time stress sigma₂The calculation method of' is as follows:

σ₂＝σ-σ₁

σ₂'＝σ'-σ₁

where σ is the initial peak stress, σ' is the real-time peak stress, σ₁The stress under the combined action of live load and constant load.

In some embodiments, the stress σ under the combined action of the active load and the dead load is determined according to the active load₁After the initial peak stress sigma and the real-time peak stress sigma' are calculated to obtain the prestress loss delta sigma of the measuring point, the method further comprises the following steps:

and calculating the residual rate mu of the prestress effect of the measuring point according to the prestress loss delta sigma.

In some embodiments, the calculation method of the residual rate μ of the pre-stress effect is as follows:

in some embodiments, the obtaining an initial strain time-course curve of the measurement point according to the distributed strain optical fiber collection, and calculating an initial peak stress σ of the measurement point includes:

extracting initial peak strain epsilon according to the initial strain time course curve, and calculating the initial peak stress sigma according to the following formula:

σ＝εE

wherein E is the elastic modulus of the concrete.

In some embodiments, the obtaining a real-time strain time-course curve of the measuring point according to the distributed strain optical fiber acquisition, and calculating a real-time peak stress σ' of the measuring point includes:

extracting real-time peak value strain epsilon 'according to the real-time strain time course curve, and calculating the real-time peak value stress sigma' according to the following formula:

σ'＝ε'E

wherein E is the elastic modulus of the concrete.

In some embodiments, the stress σ under the combined action of the live load and the dead load₁The calculation method comprises the following steps:

wherein M is₁For the moment of bending, M, caused by the dead load of the bridge to be monitored₂Bending moment, y, caused for said vehicle live load₁Is the distance, y, between the bottom of the bridge to be monitored and the inertia axis of the vehicle₂The moment of live load effective stress of the vehicle, and I is the moment of section inertia of the bridge to be monitored.

In some embodiments, the longitudinally arranging the distributed strain optical fiber at the bottom of the bridge to be monitored further comprises:

and arranging a distributed temperature optical fiber at the bottom of the bridge to be monitored along the longitudinal direction, connecting the tail parts of the distributed temperature optical fiber and the distributed strain optical fiber in series, and respectively connecting the end parts of the distributed temperature optical fiber and the distributed strain optical fiber into an optical fiber demodulator.

In some embodiments, at the initial monitoring stage and at preset time intervals, when the distributed temperature optical fiber detects that the ambient temperature of the bridge to be monitored is T, the vehicle is caused to drive across the bridge to be monitored.

The technical scheme provided by the invention has the beneficial effects that:

the embodiment of the invention provides a method for monitoring the effective prestress of a bridge based on a distributed optical fiber technology, which is characterized in that distributed strain optical fibers are longitudinally arranged at the bottom of the bridge to be monitored, the prestress calculated by data collected at the initial monitoring stage is taken as an initial value, and the stress loss generated by the prestress acting on the bottom of the bridge can be calculated by the proportional relation between the prestress calculated by the data collected at intervals of preset time and the prestress calculated by the data collected at the initial monitoring stage, so that the method has high intelligence and precision, good long-term stability and capability of comprehensively monitoring.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

Fig. 1 is a schematic structural diagram of a distributed strain optical fiber and a distributed temperature optical fiber of a bridge effective prestress monitoring method based on a distributed optical fiber technology according to an embodiment of the present invention.

Reference numbers in the figures:

1. a bridge to be monitored; 2. an optical fiber demodulator; 3. a distributed strain optical fiber; 4. a distributed temperature optical fiber.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.

The embodiment of the invention provides a method for monitoring effective prestress of a bridge based on a distributed optical fiber technology, which can solve the problems of insufficient intellectualization, low precision, poor long-term stability, difficulty in comprehensive monitoring and the like in the prior art.

Referring to fig. 1, a method for monitoring an effective prestress of a bridge based on a distributed optical fiber technology according to an embodiment of the present invention may include the following steps:

step 1: the distributed strain optical fiber 3 is arranged at the bottom of the bridge 1 to be monitored along the longitudinal direction, and in the embodiment, the distributed strain optical fiber 3 is used for collecting strain data at the bottom of the bridge 1 to be monitored, so that the distributed strain optical fiber has the advantages of electromagnetic interference resistance, strong durability, low cost and the like;

step 2: enabling a vehicle to drive through the bridge 1 to be monitored, and calculating the stress sigma of a measuring point of the bridge 1 to be monitored under the combined action of live load and dead load at the initial monitoring stage₁In this embodiment, in the initial monitoring stage and under the condition of road closure, a vehicle with a known axle weight needs to slowly drive across the bridge 1 to be monitored at a constant speed, so as to calculate the stress σ under the combined action of live load and dead load according to the parameters of the vehicle and the bridge₁(ii) a Meanwhile, an initial strain time course curve of the measuring point is acquired according to the distributed strain optical fiber 3, and the initial peak stress sigma of the measuring point is calculated, wherein in the embodiment, the strain time course curve is a curve formed by drawing measured strain values of the measuring point which change along with time in the whole process of vehicle bridging;

and step 3: enabling the vehicle to drive through the bridge 1 to be monitored at preset time intervals, acquiring a real-time strain time course curve of the measuring point according to the distributed strain optical fiber 3, and calculating a real-time peak stress sigma' of the measuring point, wherein in the embodiment, after every preset time interval, the vehicle with the same axle weight slowly passes through the monitoring bridge at the same speed to obtain the real-time strain time course curve of the measuring point at the moment;

and 4, step 4: according to the stress sigma under the combined action of the live load and the dead load₁And calculating the initial peak stress sigma and the real-time peak stress sigma 'to obtain the prestress loss delta sigma of the measuring point, wherein in the embodiment, the initial peak stress sigma is used as an initial value, the real-time peak stress sigma' is compared with the initial peak stress sigma, and the prestress loss delta sigma of the measuring point in the period of time can be obtained through calculation.

In some embodiments, the stress σ under the combined action of the live load and the dead load is determined₁Calculating the prestress loss delta sigma of the measuring point by the initial peak stress sigma and the real-time peak stress sigma' can comprise: calculating the stress sigma generated by the prestress acting on the beam bottom at the initial monitoring stage₂And stress sigma generated by prestressing the bottom of the beam at predetermined intervals_2'The prestress loss Δ σ is calculated according to the following formula:

Δσ＝σ₂-σ₂'

in this embodiment, due to the existence of the prestress loss, the prestress after every preset time acts on the stress σ generated at the beam bottom₂' phase comparison monitoring of stress sigma generated by initial prestress acting on beam bottom₂The reduction is achieved, and therefore, the subtraction of the former from the latter is the prestress loss Δ σ generated by the prestress acting on the beam bottom.

In some embodiments, the initial stress σ₂And real time stress sigma₂The calculation method of' is as follows:

σ₂＝σ-σ₁

σ₂'＝σ'-σ₁

where σ is the initial peak stress, σ' is the real-time peak stress, σ₁The stress is under the combined action of live load and constant load; in this embodiment, the data σ and σ' collected by the distributed strain optical fiber 3 are the stress generated at the bottom of the bridge 1 to be monitored under the combined action of the live load of the vehicle, the dead load of the bridge, and the prestress, so that the prestress only needs to subtract the stress σ under the combined action of the live load and the dead load of the vehicle from the initial peak stress σ and the real-time peak stress σ₁Thus obtaining the product.

Further, the stress sigma under the combined action of the live load and the dead load₁Calculating the initial peak stress sigma and the real-time peak stress sigma' to obtain the prestress loss delta sigma of the measuring point, wherein the prestress loss delta sigma of the measuring point comprises the following steps: calculating the residual rate mu of the prestress effect of the measuring point; the calculation method of the residual rate mu of the prestress effect can be as follows:

in this embodiment, the residual rate μ of the prestress effect is used to represent the stress σ generated at the bottom of the beam by the prestress action after every preset time₂' account for the stress sigma generated at the bottom of the beam by the prestress action in the initial stage of monitoring₂The ratio of (A) to (B) is the residual rate of the prestress of the stress generated by the prestress acting on the beam bottom, the distribution condition of the residual prestress of the beam bottom along the longitudinal direction is obtained, and the distribution condition is combined with the prestressThe force loss delta sigma is more intuitive and comprehensive to look at the prestress loss condition.

In some embodiments, the obtaining an initial strain time-course curve of the measuring point according to the acquisition of the distributed strain optical fiber 3, and calculating an initial peak stress σ of the measuring point may include: extracting initial peak strain epsilon through the initial strain time course curve, and calculating the initial peak stress sigma according to the following formula:

σ＝εE

in this embodiment, the data collected by the distributed strain optical fiber 3 is the strain of the measuring point, the stress can be calculated according to the strain, and the peak value of the initial strain time-course curve is taken as the initial strain of the measuring point at the initial monitoring stage.

In some embodiments, the obtaining of the real-time strain time-course curve of the measuring point according to the acquisition of the distributed strain optical fiber 3, and calculating the real-time peak stress σ' of the measuring point may include: extracting real-time peak value strain epsilon 'through the real-time strain time course curve, and calculating the real-time peak value stress sigma' according to the following formula:

σ'＝ε'E

in this embodiment, after every preset time, the peak value of the real-time strain time-course curve is used as the real-time strain of the measuring point, and the initial strain is combined to calculate the prestress loss.

In some embodiments, the stress σ under the combined action of the live load and the dead load₁The calculation method of (2) may be:

wherein M is₁Is a bending moment, M, caused by the dead load of the bridge 1 to be monitored₂Bending moment, y, caused by live load of said vehicle₁Is the distance, y, between the bottom of the bridge 1 to be monitored and the inertia axis of the vehicle₂Is the live load effective moment of the vehicle, I is the section moment of inertia of the bridge 1 to be monitored, M in this embodiment₁、M₂、y₁And y₂Can be obtained by calculating parameters of vehicles and bridges, and stress sigma under the combined action of live load and dead load is calculated₁Removing the stress sigma under the combined action of live load and dead load from the stress measured by the distributed strain optical fiber 3₁What remains is the stress that the prestressing force exerts on the bottom of the beam.

Referring to fig. 1, in some embodiments, the longitudinally arranging the distributed strain optical fiber 3 at the bottom of the bridge 1 to be monitored may further include: the method comprises the steps that distributed temperature optical fibers 4 are arranged at the bottom of a bridge 1 to be monitored along the longitudinal direction, the tail portions of the distributed temperature optical fibers 4 and the tail portions of the distributed strain optical fibers 3 are connected in series, and the end portions of the distributed temperature optical fibers 4 and the end portions of the distributed strain optical fibers 3 are connected into an optical fiber demodulator 2 through jumper wires respectively, in the embodiment, the distributed temperature optical fibers 4 and the distributed strain optical fibers 3 are symmetrically arranged at the bottom of a beam along the length direction of the bridge, the temperature is the same or close to the temperature during each measurement through the distributed temperature optical fibers 4, and the problem that the monitoring result is deviated due to the effect of the temperature on the structure is solved;

preferably, at the initial monitoring stage and at preset intervals, when the environmental temperature of the bridge to be monitored, which is measured by the distributed temperature optical fiber 4, is T, the vehicle is driven across the bridge to be monitored.

The principle of the method for monitoring the effective prestress of the bridge based on the distributed optical fiber technology provided by the embodiment of the invention is as follows:

continuously collecting distributed strain optical fiber data, and calculating to obtain a longitudinal distribution value sigma of the strain at the bottom of the beam along the optical fiber; the strain value sigma of the concrete at the bottom of the beam is sigma₁And σ₂Sum of where σ₁Stress, sigma, produced at the bottom of the beam for live and constant loads₂The stress generated by the prestress acting on the beam bottom; uniformly selecting a plurality of points (1-n) at the optical fiber monitoring position at the bottom of the bridge, subtracting the stress generated by live load and constant load action on the bottom of the beam from the peak stress of each point at the initial monitoring stage to obtain the stress value of each point under the action of prestress, and pre-stressing every otherAfter the time is set, the proportional relation of the stress under the prestress action of each point relative to the stress under the prestress action at the initial monitoring stage is found out, and then the distribution condition of the residual prestress of the beam bottom along the longitudinal direction can be calculated; the method has the advantages of simple operation, convenient implementation, low use cost and high cost performance, can directly measure and read data, obtains a result through simple mathematical operation, and reduces error calculation errors caused by multiple simplified operations (such as integral operation); meanwhile, the invention can also monitor the generation condition of the bridge bottom crack, when the beam bottom strain longitudinal distribution value is obtained by continuous monitoring, if the longitudinal distribution strain has a mutation value, the transverse crack is generated at the position of the mutation value, and the transverse crack and the position of the transverse crack can be judged according to the transverse crack generated at the beam bottom; if the strain value of a certain crack position is always larger than the value of the crack position in the continuous long-time monitoring process, the crack can not be closed.

In the description of the present invention, it should be noted that the terms "upper", "lower", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are merely for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and operate, and thus, should not be construed as limiting the present invention. Unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are intended to be inclusive and mean, for example, that they may be fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

It is to be noted that, in the present invention, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.