---

Limit to the tension reinforcement ratio ( ρ) in flexural high strength reinforced concrete (HSRC) members is based on the requirement that tension failure as sufficient rotation capacity are ensured at ultimate limit state. However, the provisions for the total amount of longitudinal reinforcement ratio ( ρ and ρ’) are not associated with any rational derivation. In this paper, a quantitative measure to evaluate an upper limit to the compression reinforcement ratio ρBmax of flexural HSRC members is proposed. The quantitative criterion to ρBmax can be derived from i) steel congestion and ii) considerations that are related to the diagonal compression bearing capacity of the members. In this paper it is shown that, when shear loading is dominant, the limit to is set by the diagonal compression criterion. Parameters that affect this limit are deeply investigated and the expressions were derived for different end conditions, to provide an additional tool for a better design and assessment of the flexural capacity of HSRC members.

---

Limit to the tension reinforcement ratio in flexural high strength reinforced concrete (HSRC) members is

based on the requirement that tension failure as sufficient rotation capacity are ensured at ultimate limit state.

However, the provisions for the total amount of longitudinal reinforcement ratio ( and ) are not associated with

any rational derivation. In this paper, a quantitative measure to evaluate an upper limit to the compression

reinforcement ratio of flexural HSRC members is proposed. The quantitative criterion to can be derived

from i) steel congestion and ii) considerations that are related to the diagonal compression bearing capacity of the

members. In this paper it is shown that, when shear loading is dominant, the limit to is set by the diagonal

compression criterion. Parameters that affect this limit are deeply investigated and the expressions were derived for

different end conditions, to provide an additional tool for a better design and assessment of the flexural capacity of

HSRC members.

---

Considering normal concrete (NC) the type of concrete need to be vibrated after placing in the formwork, Lightweight

concretes have been successfully applied in the building constructions for decades because of their low specific weight in

connection with a high strength, a high capacity of thermal insulation and a high durability. The development leading to a self

compacting light weight concrete (SCLWC) represents an important innovative step in the recent years. This concrete combines

the favorable properties of a lightweight concrete with those of a self compacting concrete (i.e., the type of concrete need no

vibration after placing in the formwork). Research work is aimed on development of (SCLWC) with the use of light weight

aggregates " Light expand clay aggregate (Leca)". In this investigation, by trial and error procedure, different mix design of

SCLWC were caste and tested to reach a so called standard self compacting concrete in fresh matrix phase such as values of

slump flow, L-box, V-funnel and in hardened phase, the 28 day compressive strength. Based on the results obtained, for two best

so-called standard mix design of SCLWC the stress-strain diagrams are drawn and discussed. Also by three different methods,

the modulus of elasticity of SCLWC are obtained and discussed here. It was found that a brittle mode of failure is governed in

SCLWC.

---

In order to lighten the prestressed concrete solid members, nowadays, it is possible to make use of the advantage of HPC (fc'>60

MPa) as well as replacing the solid section with a PSC thin-walled section for certain members such as circular and box columns.

Using the strength theory of ACI, a numerical procedure along with a computer program was developed for the analysis of such

sections subjected to axial compression or tension load and bending moments. The program solves for all possible variables such

as, concrete compressive strength (fc'= 60-100 MPa), type of prestressed steel, concrete cover, ratio of wall thickness to the section

dimensions and the PS steel arrangements to satisfy the given loading cases, thus leading to an optimal cost solution. However,

since the cross section is thin-walled circular or box and the PS steel is located at discrete points along the periphery of a circle

or rectangle, the equations of equilibrium are complex for hand computations (especially for circular section) but suitable for

computer program. So, by use of MATLAB software the interaction diagrams were also drawn for the analysis of such sections

for all mentioned variables. The use of prestressed thin-walled column diagrams is a safe and easy tool for the analysis of such

columns. Finally, the accuracy of the proposed method is demonstrated by comparing its results to those of the available

experimental values and is indicate that the proposed method predict very well the capacity of prestressed thin-walled column.