Volume 11 (2015): Issue 4 (December 2015)

The paper presents the modal characteristics of a tall building in Bucharest (BRD-SG Tower) identified from earthquake and ambient vibration records. The building was built in the early 2000’s and has a reinforced concrete structure (inner shear wall tube and perimeter frames) with 3 underground stories, ground floor and 18 stories. The seismic instrumentation of the building consists of a seismic station with two triaxial acceleration sensors located at the top of the building (+69.6 m) and at the third basement (−9.3 m). The dynamic characteristics of the building are estimated from the seismic records from 23 earthquakes (with moment magnitudes M_W between 3.7 and 6.0) that occurred during the period 2004÷2010. The results obtained from the earthquake records are compared with those obtained from 35 ambient vibration records from the period 2003 ÷ 2010.

The cement based grouts, as functional performance composite materials, are widely used for both immobilisation and encapsulation as well as for stabilization in the field of inorganic waste management. Also, to ensure that low level radioactive waste (LLW) are contained for storage and ultimate disposal, they are encapsulated or immobilized in monolithic waste forms, with cement –based grouts.

The paper includes some research data referring to cement based grout mix design for use as encapsulating/immobilizing system for low level radioactive waste. The work includes cement-based-grout mix design method used practically into establishing of the optimum grout mix based on the water/cement ratio, cement/sand ratio in order to achieve application requiered values of fluidity, segregation resistance, shrinkage and mechanical strengths. These engineering grout characteristics present relevance for simulation experiments of radionuclide leaching from LLW – cement grout encapsulation system.

Two main shortcomings of common formulations, encountered in the literature concerning the linear problems of structural dynamics are revealed: the implicit, not discussed, postulation, of the use of Kelvin – Voigt constitutive laws (which is often infirmed by experience) and the calculation difficulties involved by the attempts to use other constitutive laws. In order to overcome these two categories of shortcomings, the use of the bilateral Laplace – Carson transformation is adopted. Instead of the dependence on time, t, of a certain function f (t), the dependence of its image f^# (p) on the complex parameter p = χ + iω (ω: circular frequency) will occur. This leads to the formulation of associated non-classical eigenvalue problems. The basic relations satisfied by the eigenvalues λ_r^#(p) and the eigenvectors v_r^#(p) of dynamic systems are examined (among other, the property of orthogonality of eigenvectors is replaced by the property of pseudo-orthogonality). The case of points p = p’, where multiple eigenvalues occur and where, as a rule, chains of principal vectors are to be considered, is discussed. An illustrative case, concerning a non-classical eigenvalue problem, is presented. Plots of variation along the ω axis, for the real and imaginary components of eigenvalues and eigenvectors, are presented. A brief final discussion closes the paper.

The present paper presents the structural and seismic retrofit solution for the structure of the Catalytic Cracking Reactor, from Petrobrazi Refinery, Ploiești, Romania. The spatial truss type steel structure was designed and built during 1965-1968, following United States codes of that time. The capacity of the reactor is intended to be increased, thus its weight increases by approx. 43%. The retrofit solution had to take into consideration many criteria, not only technical, but also technological. After analyzing several possibilities, it was decided that the only feasible solution in order to fulfill all these requirements was to significantly increase the viscous damping of the structure – by introducing viscous dampers in its diagonals, accompanied by the strengthening of steel structure and changing the structural system into a moment resisting frame.